Throttle stuck open!

5th March 2008, 08:16

Chaps...

I had a real fight on my hands trying to drive home last, nightmare! Whatever RPM I took the engine to, as I disengaged the clutch to change gear, the revs were just staying there. Not good when you come to a standstill, and the engine is screaming at 6000rpm!

Typically, after about 5 seconds, the revs would drop, but they wouldn't stop nicely at just under 1000rpm, they would just keep falling, and the car would stall.

I manged to get home in one piece somewhere, so it was inspection time.

I could only assume a sensor such as the TPS was on the piss. I believed this sensor to be located on the back of the throttle body. So I thought the best course of action was to take the sensor off and clean it... Only problem, one of 2 screws holding the sensor in, was at an unbelievably difficult angle to get at, and the fitment was one of those stupid star shape thingies. After I thought I'd exhausted all my options with no dice, as there was no room for a socket to get at the screw, I found a screwdriver with the correct star shape. Still, no good as the bulkhead is in the way, however, with a vice and a blowtourch,

I manged to turn the screw driver into a right-angled one! lol.

So, sensor was soon out, and I was pretty shocked at what I saw. It was completely cacked in thick, jet black shyte, just like what you find inside the throttle body. I cleaned it all up, so it looked spanking new, and also the inside of where the sensor was located. All back together... Started the car up, and for the first 5 seconds it coughed and splattered and had to rev it, but soon after it was spot on. The car a had a good run this morning and it was tip top.

So if anyone ever has a similar problem, it's definately worth giving this sensor a check.

5th March 2008, 08:20

I had a similar problem but with the ICV, The car would rev all over the place and just die.
Tried cleaning but the icv was nakered

You should make a guide.

5th March 2008, 08:26

AH, so was it the ICV I sorted or the TPS? lol

5th March 2008, 08:30

lol, did it look like this?

5th March 2008, 08:49

Almost identical. The only difference is the tip. The tip on mine was plastic, and the shaft was steel. The housing looks identical though.

5th March 2008, 08:50

thats the icv

, the tps is under that (And probably harder to remove).

5th March 2008, 09:05

Funnily enough, I thought it was the ICV at first. But when I took it out, it appeared to me that it looked more capable of determining the throttle position as opposed to the controlling the idle. Any idea how it works?

5th March 2008, 11:48

Good stuff Toad, glad to hear its sorted..

I'll agree, that sensor is a twat to get off..I'd love to punch the bloke who designed it..

5th March 2008, 12:16

I would love to punch him too

all the problems we have ran into have been idle setting related lol.

For anyone who is interested this is how it works.

Its proper name is an IAC Valve, standing for Idle Air control. Its basically a DC motor, inside are coils, some have one some have two, the varient on the VTS is 2 coils, meaning its a 4 wire IAC. The ECU turns the motor in "steps" from 0 to around 255. the more steps, the less "idle" air is entered into the engine, when its stone cold, it'll be around 130-150 steps, allowing loads of air in for cold start, and as the engine warms up a closed loop algorithm senses the coolant temp rising and shuts the valve slowly until fully warm is around 200 steps.

Hope this helps

Ross
RCD.

5th March 2008, 12:19

I had this, was the accerator cable, it was severd, had to set the rev manually and drive to the garage in 2nd
was great fun

5th March 2008, 12:24

How could a broken cable make it rev high mate? or are you talking about something else.

Ross
RCD.

5th March 2008, 12:25

Quote:

Originally Posted by RCD-Performance

How could a broken cable make it rev high mate? or are you talking about something else.

Ross
RCD.

driving along and in second and the accelrator just dropped ot the floor, had to pop it out gear.

cable looked fine from the engine but half way down it was seved and not relaesing

garage sorted it out in ten mins

5th March 2008, 12:26

ahhh i see mate! There normally very reliable, one of those things you don't really think about!

Ross
RCD.

5th March 2008, 12:54

Quote:

Originally Posted by RCD-Performance

I would love to punch him too

all the problems we have ran into have been idle setting related lol.

lol

My Torx set are a tiny bit too long and hit the bulkhead which makes it soo fooking fiddly..

5th March 2008, 12:55

Quote:

Originally Posted by RCD-Performance

I would love to punch him too

all the problems we have ran into have been idle setting related lol.

For anyone who is interested this is how it works.

Its proper name is an IAC Valve, standing for Idle Air control. Its basically a DC motor, inside are coils, some have one some have two, the varient on the VTS is 2 coils, meaning its a 4 wire IAC. The ECU turns the motor in "steps" from 0 to around 255. the more steps, the less "idle" air is entered into the engine, when its stone cold, it'll be around 130-150 steps, allowing loads of air in for cold start, and as the engine warms up a closed loop algorithm senses the coolant temp rising and shuts the valve slowly until fully warm is around 200 steps.

Hope this helps

Ross
RCD.

That's interesting, thanks for the explanation. Question however... How do you think this device could have caused the symptoms I described? Such as the revs staying at what RPM I was doing, and when they eventually fell, it wouldn't remain just below 1000rpm, it would just drop and stall the engine.

5th March 2008, 12:58

Quote:

Originally Posted by James_Bristol

lol

My Torx set are a tiny bit too long and hit the bulkhead which makes it soo fooking fiddly..

Try the blowtourch method mate!

5th March 2008, 13:00

Haha..My do next time..

5th March 2008, 13:06

Quote:

Originally Posted by Toad

That's interesting, thanks for the explanation. Question however... How do you think this device could have caused the symptoms I described? Such as the revs staying at what RPM I was doing, and when they eventually fell, it wouldn't remain just below 1000rpm, it would just drop and stall the engine.

If theres lots of shite on there, the ECU could say to the IAC "move" and it wont, cos its bunged up, then if it frees it might move too much, giving too much or not enough air!

5th March 2008, 13:18

Ah, so it actually has air going into it. I didn't realise that. When I inspected the sensor, the only thing I could see that moved was the plastic, cone shaped tip. This tip piece also seemed quite loose, as in, it was easy to pull back and forth, as if it wasn't on a spring or anything. Is this normal?

The other question I had was to do with the sheer amount of black stuff. I've noticed the same stuff on the inside of the butterfly and in the inlet manifold. I guess this is probably to do with the cams and the overlap, and air not having much option but to go back the way?

5th March 2008, 13:22

The sensor's we've encountered do move move by hand, maybe the 106gti sensor is different i don't know mate. basically that tip moves in and out, allowing more or less air to pass through the ilde chamber. It doesnt have air going in to it so to speak, but air passes over it. I.e when its fully out, its seated and no air can pass, but this never occurs normally.

With regards to the "black shit" its simply residue, remember the rocker cover oil breather feeds into the TB, hense any atomised oil will enter, mix with air, and the moisture in the air to produce that stuff

5th March 2008, 13:29

Got you about the sensor!

The black stuff is only located after the butterfly though. Everything on the outside is clean as a whistle. I don't route my breather back into the induction...

Every now and then I give my air filter a clean, so I take off the induction kit etc. If I open the butterfly, the inside of it is always covered in black. Lord knows what the inlet manifold must look like!

5th March 2008, 13:33

Hairy one Toad, i bet mine is pretty crap covered atm too. Every now and then when i slow down to stop at lights thre revs sit about 1500/2000 rpm. With the handbrake on i just let the cluch out a bit so the engine labours a little and brings the revs back down.

Will have a check of that sensor tonight!

5th March 2008, 13:45

Mine was slightly different I think. If I booted it in 2nd to 6500rpm, and then took my foot off the gas, the car would keep going for it!

If disengaged the clutch, the revs would just stay there as if the accelerator cagle was sticking. After a few seconds, the revs would finally drop, but they would drop all the way and the car would stall. It was really hard to keep driving. And I got some funny looks while sitting at the lights @ 6000+ rpm! LMAO.

Good luck getting the sensor out mate. You'll need a star fitment, but on a right angled tool... You'll see what I mean when you try to take it out. :d

5th March 2008, 13:50

Enjoy is Mystic, its such a fun job you'll love it!

5th March 2008, 16:07

I just popped down to a local car accessories shop, Got some torx allen key things.

6th March 2008, 13:22

Quote:

Originally Posted by James_Bristol

lol

My Torx set are a tiny bit too long and hit the bulkhead which makes it soo fooking fiddly..

It's much easier just to take the whole throttle body off. Access to the Idle control valve (and TPS) is then very easy. You can then also easily clean out the orifice that it goes in as this is usually gunged up too.

7th March 2008, 18:47

A rather long update chaps, so please bare with me...

Unfortunately the problem reared its ugly head again the following day after cleaning the IAC valve. I had to drive to Cheltenham (about 2 hours) to go see about the problem I've got with the brakes, another LONG story!

Anyway, en route to Cheltenham the problems started occuring again. The revs seemed to stick and the car wouldn't slow down when you came off the throttle. When I came to a standstill, the revs would eventually drop, but lower than normal, and it would struggle to tick over. Well, after about 1 hours driving, I had to stop for fuel. When I got back in the car, the problem was compeltely gone.

Later on when I left Cheltenham, the problem started again... So I decided to bite the bullet and buy a new sensor ASAP. In the meantime, the problem was pretty constant, so I couldn't wait to get the new sensor fitted!

I picked the sensor up today. When I opened it, I noticed it was very, slightly different to the current one. The screws were also a different fitment, so to fit it, I had to use the original ones. Wierd... Anyway, popped the new IAC valve on no probs, started the engine, and the revs shot up to 3000rpm and stayed there.

I stopped the engine, started it again, and it was the same. On the 3rd attempt, it seemed a little better, more around 2000rpm, but it was still sticky. I got on the blower to Pug and explained the issue. They checked the part numbers and assured me it was the correct for my chassis number. They mentioned that ECU might need a reset when this sensor is replaced, but they weren't sure. I got in the car, and went for a quick test drive. It wasn't too good, very similar to the way it drove with the previous sensor. I nearly crashed it when trying to come back into my driveway, as when I disengaged the clutch, the revs shot right up to the limiter, and I had to turn the engine off to stop it!

So, thinking time... Could it be an air leak? Not sensor related at all? I had a thought that if I take off all the induction kit, so I can view the butterfly openeing and closing... If the revs stick up high and the TB is closed, then this will be a sure way of proving I've got an air leak. So I did just that, but when I fired up the engine this time, it was idling much more like normal, although still rough. Hmmm. I looked at the butterfly as I was opening the throttle and the revs weren't sticking at all, so I couldn't prove whether there was an air leak or not! Damn it!!! Grrr. Anyway, while the engine ticked over, it was still struggling to idle, but it seemed to get better. Every time it was just about to stall and the engine shaked, you could hear a "hiss" as more air was sucked in and it idled OK for a moment. I would say every 5 - 10 seconds you heard the "hiss". When you heard this "hiss" noise, the butterfly didn't move, so I assume air was being sucked in through that small hole above the butterfly... ?

I took the car for a spin with no air filter on, and it was fine. The revs weren't sticking, and it wasn't stalling. I popped the air induction kit back on, and it was still fine. And that's where I'm up to now. The car seems OK now, I'm totally lost.

I'm going to leave it for a few hours, so it's totally cooled down, and then fire it up again and see if it's still happy. I wonder if the ECU has learned the new sensor?

Anyone's views / comments would be appreciated.

7th March 2008, 19:50

I had the same problem, the new sensor came with self tapping screws so used the original ones.
I cant remember now but did your new IAC come with a rubber ring seal?

You could try unplugging the battery for an hour, then turning the ignition with out starting the engine 4 times, let the ECU learn.

7th March 2008, 20:20

i have heard that it you fit a new iac you need to turn your ignition on and off a cuple times so it sets the IAC up then it should be fine

7th March 2008, 20:35

Thanks guys.

It seems as if the ECU has been trying to learn... I didn't realise this was the case. Fingers crossed it will be OK.

It did come with a rubber seal, yep.

8th March 2008, 08:03

Had a long run in the car today and the problem still persists. Nothing has changed. In fact, it's getting worse if anything. Could it be the throttle position sensor?

8th March 2008, 08:32

It could be, but there generally very reliable. Thats a wierd one mate.

8th March 2008, 08:56

IS there like a stepper motor of some sorts? Something that helps it tick over on idle besides the IACv? Like an automatic choke?

8th March 2008, 08:57

Pulling my hair out. Not looking forward to my journey out of London today.

8th March 2008, 10:19

That is strange, The new one fixed my problem.
Have you tried leaving the battery off an hour then turning the ignition 3 times yet?

8th March 2008, 10:58

Yeah dude. I'm at work now, so I might go take the battery off and leave it for a good 8 hours...

I've been on the phone to Pug again, and the head mechanic seems to think it likely to be a faulty stepper motor. Apparently, if the stepper motor is working flat out, it will cause the revs to raise in the manner I have mentioned. The rough idle could also suggest the stepper motor isn't functioning correctly. I've got one on order... I haven't got great faith that this will resolve the problem, but I'll keep you all posted anyhow.

8th March 2008, 11:01

Quote:

Originally Posted by Alex

That is strange, The new one fixed my problem.
Have you tried leaving the battery off an hour then turning the ignition 3 times yet?

One other think Alex, did you definately have the exact same symptoms as I've got? I'm having to keep the car in gear when coming to a standstill, and applying the brake to slow the car down. If I just pooped it out of gear, or disengaged the clutch, the revs would start to raise quite sharply. When I get the car to a standstill, the revs do drop, but the idle is really bad. It idles between 600 and 1200rpm, so it almost stalls, and then picks up again... The tachometer is waving up and down.

8th March 2008, 11:15

alright toad you got a picture of what you removed looking into the engine bay at the throttle body, my mate alex_vts on here is having a similar problem.

and im going to be seeing him today so while im at his ill remove this get it cleaned up and put back together

8th March 2008, 11:23

Probably not a lot of point just yet mate, as it's not certain it's the IAC valve that's causing the issue. I'm at work, so I can't upload a pic anyway...

The IACv is located to the rear of the throttle body. It has a 4 pin plug attached also, and is held in place by 2 star headed screws, you can't miss it.

8th March 2008, 11:43

Hang on a sec, the stepper motor is the IACv. What a joke. I told the mechanic at Pug that I had replaced the IACv and the problem was still occuring, and I was told to try changing the stepper motor, but it's the same bloody thing! What's this world coming to?

8th March 2008, 12:07

Right, humour me for a seconds guys. Why is it that when I'm driving on the motorway, and I come off the throttle, the car doesn't slow down / revs stay up, yet if I'm under the bonnet, reving the engine by the throttle, (car obviously isn't moving) the revs don't stick at all? Is there a sensor that reads the speed in which the car is travelling at, so it knows what the idle should be if you come off throttle while hurtling down the motorway at 80mph+ for example... ? Do you see where I'm getting at here? IIRC, the idle shouldn't drop down to like 800rpm if you put it in neutral at 100mph, should it?

8th March 2008, 12:23

If not in gear it will drop down to idle.

The problem first occured on mine after i left the motorway, got to the end of a sliproad and engine just cut out, then when i come of the accelerator the revs would stick, drop down to 500 odd nearly stall then bounce back up.

I tried a second hand iac, worked for a few days then started again so got a new one.
One thing i did do is spray some card cleaner in the hole where the iac is, then shoved a cloth in there to clean it, lots of black dirt was coming out.

8th March 2008, 12:43

I shoved a cloth in the same hole mate. I didn't use any cleaner though. Was it a carb cleaner?

8th March 2008, 12:48

I just fired the car up and left it idling for about 10 mins. I revved it from the drivers area using the pedal, and also from under the bonnet. I couldn't get the revs to stick in any way shape or form. The idle was fine too, there was no hunting, all seemed pretty good. Will it be like this when I'm actually on the road driving it though? Hmmm...

This is exactly how I left the car last night, all seemed fine. But this morning on the way to work, it was a nightmare!

8th March 2008, 13:11

Guess you will have to wait till the journey home.
And it was carb cleaner, not card cleaner

8th March 2008, 13:54

Alex, going back to this carb cleaner stuff. If you open the butterfly and peak inside, mine is caked in black soot like stuff, which is also a tad oily. Is this a bad sign?

8th March 2008, 13:56

I would say it's normal, mine was the same, remember that the stock induction had the oil breather feed, so theres bound to be a little oil & grime residue.

8th March 2008, 14:39

Mine seems to be sticking at 2k rpm again..You take your foot off the throttle and as soon as the revs drop to 2k rpm it just sticks and carry's on driving on its own..Cruise control tbh..

If i put the clutch in the revs finally drop to 1500 rpm but then bounce up and down between 1500-1750 rpm..

I have cleaned all of it out and stuff, my Stepper Motor/ICV was only replaced about 15k ago..

Sometimes though its absolutley fine, also the car has just developed a slight knocking from the front drivers side, not CV joint, think its a balljoint of some kind..

Damn car's..

8th March 2008, 14:44

@James, Could be your temp sensor, had the same problem on my old 1.4, would rev at 2k and bounce around some times, i changed the temp sensor on that the other day, my mate said it hasn't happened since.

8th March 2008, 14:56

Oh right..

Will get one on monday..May aswell give it ago..lol

Cheers dude..

8th March 2008, 14:59

Think it was £16 from a dealer near me, So cant hurt to try, if it still does it after just ebay the new one

8th March 2008, 15:16

I'm honestly inches away from buying a set of iTBs and some proper management kit. I could kiss goodbye to all of this malarky!

8th March 2008, 15:27

Quote:

Originally Posted by Toad

I'm honestly inches away from buying a set of iTBs and some proper management kit. I could kiss goodbye to all of this malarky!

Sounds like a plan, would cost a bit more than a stepper motor tho

8th March 2008, 15:30

Quote:

Originally Posted by Alex

Sounds like a plan, would cost a bit more than a stepper motor tho

TRUE!

Although i guess it would be more fun getting your car back from the garage ahving iTB's fitted and mapped, than a new IAC< BORING! lol

8th March 2008, 15:37

Already fitted the new IAC mate, and yeah, very boring indeed, as it's still shit...

8th March 2008, 15:43

lol, iTB's it is then

8th March 2008, 15:45

Maybe mate. But I do need to get the car working properly first. So this one isn't over by a long shot. I need to get the car sticking in the revs, and then quickly look at the butterfly to see if it's sticking open. I can't comprehend why it's not happening unless the car is in motion! WTF.

8th March 2008, 15:58

I wouldn't have thought the butterfly would be getting stuck, the spring is pretty strong. It must be the IAC, just strange a new one didn't fix it.

8th March 2008, 16:04

You really think? The issue with the high revving after the new IACv went in was resolved last night. It just took a few stops and starts before it dialled itself in. The original problem hasn't altered a bit in all honesty. In fact, it was worse this morning than ever before. When I was in 3rd at 30mph, if I took my foot off the throttle, it actually started to speed up!

And when I came to a stop, the idle was shocking! Constantly trying to stall... I had to keep bliping the throttle to prevent it.

8th March 2008, 16:14

Could be a vacuum leak, did you say you have another stepper motor coming? Might just have to wait till it arrives and try that.

8th March 2008, 16:20

Nah, didn't realise IACv and stepper motor where one of a kind, order is cancelled.

If it were a vacuum leak, I would be able to see the engine rev and at the same time, see the butterfly remain closed. Unfortunately, whenever I go under the bonnet to check this, I can't get the revs to stick, lol. As I said before, they only seem to stick when the car is in motion.

8th March 2008, 16:33

Wierd, cant see how the car moving could affect it.

8th March 2008, 17:01

Quote:

Originally Posted by Alex

Wierd, cant see how the car moving could affect it.

Load on the engine?

im puzzled by this Toad

We had similar problem on our demo car, but that was the aweful start up map! So easily rectified.

8th March 2008, 17:13

Quote:

Originally Posted by RCD-Performance

Load on the engine?

im puzzled by this Toad

possibly, i'm stumpted too

8th March 2008, 17:23

I'll keep playing about, see what I can find. I might try disconnecting the power to the IACv, see if that changes anything at all.

8th March 2008, 23:25

Update chaps...

On leaving work, the car seemed fine, it was all acting as normal, but about 20 minutes since I set off, things started playing up. The car wouldn't drop the revs again, and whenever I came to a standstill, the car was hunting between 700 and 1200rpm. For about the next 30 minutes, it was pretty much constantly playing up, only on the odd occasion would the revs drop like they should.

I decided to have a little play on the motroway, as the roads were dead quiet. When at about 4000rpm in 5th gear, I let off the throttle and pushed the clutch pedal down, and the revs climbed to 5000rpm, stayed there for about 5 seconds, and then all of a sudden, the revs shot right up to 7000rpm, just as quick as if had floored the throttle. They then stayed there for about another 5 seconds, and then dropped back to normal idle speed! So strange...

As I was coming off the motorway, I came to a set of traffic lights. I slowed down in 4th until the revs were at about 2000rpm, and then I put the gear into neutral and stopped the car. The revs then shot up all the way to 7000rpm again, and I wasn't even moving!

The only way I could stop the revs was to put it in gear, and use the clutch to force the revs down. Once the revs get low enough, they don't seem to try and climb.

Once I took off from the lights, I had about a 10 minute journey left to get home, and in that 10 minutes, the car was absolutely perfect. After stoping at a few other lights, the idle was spot on, and the revs were dropping as normal. I pulled up to my driveway and stopped the car but left it running. I then gave the car loads of revving and it was absolutely fine! Arggg!!!

So here's my diagnosis, lol. :d I don't think the IACv can make the revs shoot up so significantly as what happened when I was on the motorway. It seems odd how when this problem is happening, I also have the bad, hunting idle. So I reckon this is down to the TPS giving incorrect information to the ECU. Think about it, if the revs shoot up on their own accord, this could be the TPS thinking the throttle is not open, and when the idle is really struggling, this could also be the TPS saying the throttle is open. What do you think?

8th March 2008, 23:31

The IAC can do that mate

When testing our first ECU, we managed to wire up one of the IAC coils the wrong way round, (4 wires the same colour didnt help!) So when the ECU said *fully open* it *fully closed* and vice versa, this made it *idle* at just over 7k RPM.

I am starting to suspect an ECU fault, as that is what controls all these things. We had many problems with hunting idle, high idle, then it would be fine, 100% the same as the problems you are having, when we were testing the ECU. Although i cannot for the life of me see why your car would do it just like that.

If you wern't so far oop north i would come over and have a ganders our of curiosity mate!

Ross
RCD.

9th March 2008, 00:00

I didn't realise the IACv could do that, that's interesting! Well, I won't be using the car to get to work tomorrow, that's for damn sure. Just to be thorough, I've unplugged the battery just now, so it will be off for at least 24 hours.

I really hope it's not an ECU fault.

I've plugged the ol' diag reader, and it's not telling me anything new.

If I had an air leak, surely it wouldn't be fine one minute, and then completely tits up the next? I think I will try to take the TPS off next, and give it good clean. If that doesn't help, I will take the whole inlet manifold off and completely clean it out, as it's got loads of soot inside it anyway. I can then make sure it's properly attached to the head, and there's no signs of any leaks etc.

Thanks for the kind offer mate. I'm about as useless a mechanic as humanly possible, so any expert advice would (and is) very much welcome!

I don't live that far up north you know, I'm not far from london mate.

9th March 2008, 00:11

I don;t think its an air leak fella. And i don;t think the TPS could do it, as if its full of crap, the only thing it can do is give no reading. Also, if the butterfly valve is not moving, thres no more air going in the engine, so it cannot rev higher, as the IAC controls the air, so my guess its definately an IAC/ECU related issue, i've sent you a PM

Ross

9th March 2008, 08:53

Another update, as I couldn't resist using the car to get to work this morning, lol.

I had the battery disconnected for about 12 hours by the time I fired her up this morning. It certainly made a "difference." The revs went up to around 2500 on start up, just like what happened when I first replaced the IACv. I stopped the engine, and fired up again, this time the revs fell too low, and it started hunting again, going from the likes of 600 to 1200rpm. I needed to get going anyhow, as I would be late...

For the first few mins, the car was pretty shit, but it then got itself into gear. And to be fair, for the next 30 mins of driving, it was absolutely spot on. When coming off throttle, there was a nice feeling of the car slowing down, it felt nice and tight.

But alas, it didn't last. The last 15 mins of my journey were the same old story... Pulling up at traffic lights, and if I didn't use the gears to bring the revs down to below 2000 rpm, while I was not even moving, they would just start to fly up, nightmare. And when I did get the revs to drop, as I was sitting there idling, it would be hunting real bad again.

I got to work, with not a lot of time on my hands. While I was parked up, it was still hunting badly. I turned the engine off, and took the connection out from the IACv. I then started the car up and the revs jumped to 2500rpm, lol. Perhaps not the best idea, but I was just curious what it would do.

I then plugged it back in, making sure it was firmly seated, started the engine, and the idle was perfect, lol. Sitting about 900rpm (this is normal for my car) nice and lumpy because of the cams

but the tacho was dead still just like it would normally be. It's a mystery alright. Could it be a wiring problem? The connection from my loom which goes into the IACv looks fine, it's spotless. I suppose I could pinch the connection bits inwards to give it a tighter fit, but it certainly doesn't need cleaning.

9th March 2008, 09:49

You could have just been unlucky and got a faulty IAC valve, After i cleaned my original one it would work fine for a while, then the same problems started to occur.
I can only suggest you get pug to swap it over and see if another new one fixes it.

9th March 2008, 10:44

Maybe mate. It's certainly not the same as the original one anyhow. You know how the sensor has like a black coloured plastic end to it? Well my original one had this, but then the rest of the cylinder was like stainless steel. The new one is all black and all plastic. The new one is also a teeny bit bigger... Pug said it's definately the correct part for my chassis number.

9th March 2008, 11:54

Sensors an arse to get off? Hahahaha.
Take the induction kit off and it's 3 bolts to take the whole throttle body off and then you have easy access to all sensors and you can clean the throttle body itself out too. 10 mins, minimal tools, no stress.

9th March 2008, 11:56

Cheers dude. I may try taking the whole inlet mani off...

9th March 2008, 11:57

As for your problem i've only skim read the thread, sounds like it's misfiring. Have you managed to find a set of circumstances that can replicate the problem?
Sounds like it's running really rich if it idles very high and bogs down at idle, coolant temp sensor would be my guess, it only does it when the engine gets hot, and that goes with it only doing it late in journeys but fine from cold start, mine only did it when it got over std temp(when sitting in traffic), get the multimeter out and give it a test when cold, warm, hot and very hot.

Edit; Don't take the whole manifold off, there's nothing of interest to you in there, the map sensor is the only other sensor, the injectors live under the top half but it doesn't sound like them to me.

9th March 2008, 12:15

No mate, I can't find a set of circumstances that replicate the problem, it seems to be completely intermittent. The temperature of the engine doesn't seem to have any direct relation to the issue. Similar to what happened this morning, when I got to work and parked up, the idle was horrid, hunting badly. I stop the engine, disconnected the connections to the IACv and plugged them back in, and the car idled absolutely perfectly. For more than half of the 1 hour journey, the car was behaving perfectly, it was slowing down properly when off the throttle...

9th March 2008, 12:23

I think my best thing to do next will be to clean the hollow out which the IACv is housed, and make sure air can flow properly to the IACv.

9th March 2008, 12:23

Yeah mine started off totally intermittantly, then eventually the problem started to occur under certain circumstances after a good while.
I replaced: ICV, MAP and IAT sensors before i got my multimeter out and found the real problem.

9th March 2008, 12:24

The idle control valve shouldn't be able to let enough air through for it to idle at 2.5k, only around 1.5k if it was stuck open.

9th March 2008, 12:30

According to Ross, the IACv can make it idle anywhere, as they put the connections in the wrong way around by mistake and the revs went all the way up to 7000rpm... But I originally thought what you do...

I replaced my coolant temp sensor just 3 days as well. This problem occured 2 days before I changed the coolant temp sensor, so I would have thought it would be fairly safe to assume that the coolant temp sensor is working OK...

So the question is, what sensor can make the revs go from 2k to 7k just as fast as if you opened the throttle by booting it?

9th March 2008, 12:45

you won't get enough air through that tiny passage to carry the car up to 7k rpm, simple as.

Are you sure the throttle isn't actually sticking? However if it was then that wouldn't explain the dropping revs below idle.

Pug techs told me how to reset the ecu properly.
Half hour with battery off, twist idle control valve in(as it would be when new)
Turn ignition on, leave at 2nd click for 30 seconds.
Start car without using accelerator, let idle till the fan kicks in, then the rest of the adaption comes from driving it.

Air temp sensor could explain stalling. Only other thing that controls fuelling lots is the TPS or map sensor, have you tried borrowing someone elses? i sold my spare ages ago. I would rule out the injectors for now.

9th March 2008, 13:06

So are you saying that the IACv cannot tell the ECU to open the butterfly? - I thought this was how it worked...

What do you mean by "twist" the IACv in?

EDIT: If the car will rev from 2000 to 7000 on its own accord, something must be controlling the butterfly other than the throttle correct?

9th March 2008, 13:24

The IACv just goes in and out, doesn't affect the butterfly.

When i first fitted the new IACv on mine i started the car, it would rev to 4k and stay.

9th March 2008, 13:31

Mine went to 3k when I first installed it. But doesn't this mean that this sensor is capable of increasing the revs / opening the butterfly? OR, can it allow enough air into the inlet (bypassing the butterfly) to rev to 7000?

9th March 2008, 13:42

I'm not sure what revs it's capable of achieving, As AlexR said it's a small hole.

9th March 2008, 13:43

Quote:

Originally Posted by Toad

According to Ross, the IACv can make it idle anywhere, as they put the connections in the wrong way around by mistake and the revs went all the way up to 7000rpm...?

Yes it can

Quote:

Originally Posted by Toad

So the question is, what sensor can make the revs go from 2k to 7k just as fast as if you opened the throttle by booting it?

IMO, the only sensor that can do this is the IAC, although another sensor could be giving a intermitant ready, amaking the IAC shoot open. It takes around 1.5secs for the IAC to go from fully open to fully closed.

Toad, i have new coolant temp and AIT sensors, and an IAC valve sitting here, PM Sent with regard to diag

Ross
RCD.

9th March 2008, 13:45

[QUOTE=AlexR;1946693]you won't get enough air through that tiny passage to carry the car up to 7k rpm, simple as.

[QUOTE]

I'm sorry mate but yes it can.

Quote:

Originally Posted by Toad

So are you saying that the IACv cannot tell the ECU to open the butterfly? - I thought this was how it worked...

What do you mean by "twist" the IACv in?

EDIT: If the car will rev from 2000 to 7000 on its own accord, something must be controlling the butterfly other than the throttle correct?

The ECU cannot control the butterfly, only the throttle cable does this.

The IAC is a screw driver stepper motor, so it "twists" to allow it to go in and out.

9th March 2008, 14:36

So was I supposed to do something else with IACv? I just put the rubber ring around it and attached it on so it was nice and tight, nothing else...

So is the IACv more of a mechanical part as opposed to a sensor? I.e., does something else tell it when to do its thing?

Cheers Ross, replied to mate.

9th March 2008, 14:48

Quote:

Originally Posted by Toad

So was I supposed to do something else with IACv? I just put the rubber ring around it and attached it on so it was nice and tight, nothing else...

So is the IACv more of a mechanical part as opposed to a sensor? I.e., does something else tell it when to do its thing?

Cheers Ross, replied to mate.

The ECU controls the IAC, its a valve not a sensor

It has no feedback to the ECU at all

Replied

Ross

9th March 2008, 15:16

Ah, so obviously I'm going to ask... What tells the ECU to alter the IACv? lol

9th March 2008, 16:17

lol thought you may ask that.

If the engine is cold the ECU adds a percentage of extra fuel and air, and the IAC valve meters the extra air, as the engine temperature comes up, less air and less fuel are needed for a good solid idle so the ECU cuts back on the idle fuel and cuts back on the air by pushing the IAC valve closer to its seat

Ross

9th March 2008, 16:38

Cool, so I've either got a faulty coolant temp sensor or a faulty IACv. Funny though, as both have been replaced after the problem occured. Grrr.

9th March 2008, 16:53

Yeah i remember you saying, which is why its puzzled me so much. However i'm sure we'll sort it

9th March 2008, 17:13

To answer your question - what tells the ecu how to adjust the ICV, the map sensor tells the ecu how much air there is passing through the plenum, the coolant temp sensor says what temp the engine is so it knows what temp correction to use, and the crank sensor tells the ecu how fast the engine is spinning so it can adjust the valve to maintain a smooth idle speed.
The idle control valve opens at 1500rpm as std.

9th March 2008, 17:13

I bet if you opened the valve and unplugged it that the car wouldn't idle at 7k.

9th March 2008, 17:17

How do you mean it "opens" at 1500? The IACV is a constant correction valve there is no set point for it to open.

It wouldnt idle at 7k with it off no, as the ECU would sense no resistance from the coils

9th March 2008, 17:19

I mean the idle control valve is activated at 1.5k on a standard ecu, you can even feel it. It's not a constant correction valve, it only works on overrun and idle.

9th March 2008, 17:23

Quote:

Originally Posted by AlexR

To answer your question - what tells the ecu how to adjust the ICV, the map sensor tells the ecu how much air there is passing through the plenum, the coolant temp sensor says what temp the engine is so it knows what temp correction to use, and the crank sensor tells the ecu how fast the engine is spinning so it can adjust the valve to maintain a smooth idle speed.
The idle control valve opens at 1500rpm as std.

Blimey! Cheers Alex. This brings a lot more parts into the equation.

Something I've noticed just from being a bit anal in the past, but it might make for an interesting point...

If I was travelling at speed, and just disengaged the clutch, or popped it into neutral, the revs would not go down to the normal idle rpm of 900, in fact, they would sit more at like 1200rpm if I was doing say 70mph. So something knows that the car isn't stationary, hmmm?

9th March 2008, 17:24

Quote:

Originally Posted by AlexR

I mean the idle control valve is activated at 1.5k on a standard ecu, you can even feel it. It's not a constant correction valve, it only works on overrun and idle.

"Overrun and idle" - The 2 areas I have the problem! Coincidence?

9th March 2008, 17:26

Quote:

Originally Posted by RCD-Performance

Yeah i remember you saying, which is why its puzzled me so much. However i'm sure we'll sort it

Fingers crossed mate!

They'll definately be a good drink in it for you!

9th March 2008, 17:37

I would say that if it only occurs at overun and idle then the tps isn't telling the ecu that the throttle is shut so the valve stays open.

9th March 2008, 17:55

So the TPS could at fault?

9th March 2008, 17:57

Quote:

Originally Posted by AlexR

I would say that if it only occurs at overun and idle then the tps isn't telling the ecu that the throttle is shut so the valve stays open.

The valve has no feedback from the TPS, it constantly moves when the engine is running to correct the idle, even if the engine is not idleing, so that when it comes back to idle (Throttle shut, 20kpa ish map) the engine idles correctly.

The iacv NEVER shuts. if it did this, the car would stall when the driver disengaged the clutch and shut the throttle all the time.

9th March 2008, 18:05

If the area that houses the IACv is not clean, and in my case, may be blocked up, would this be a possible answer to the problem?

When I took the original IACv off, it was totally caked in soot, a good couple of mm think too. I showed cloth down the housing to try and clean things up, but as it's at such a crap angle, I couldn't peak in to see what was what.

9th March 2008, 18:07

I beg to differ. Anyway toad it's up to you what you do.
The ICV will react to the tps, if the throttle's open then it will stay in a set position(open) so that the only thing varying the inlet charge quantity is the throttle plate itself, when the throttle plate is closed then the ICV will adjust to allow the correct amount of air to bypass the throttle plate for either overrun or idle. How do cars idle with standalone and no ICV control? they close the icv so no air bypasses the throttle plate, then the throttle stop is adjusted to allow the required amount of air through.

If the car has a new ICV and it is still acting the same surely it indicates that something else must be at fault? And if the ICV is acting strangely maybe this is because the ecu is telling it to, which means that whatever is telling the ecu how to control it is faulty.

9th March 2008, 18:08

Not really, they get caked in crap after about 10k and seem to work fine. spraying lots of carb cleaner through the throttle body is a good way to clean it. I took mine off to clean it out.

9th March 2008, 18:13

Interesting stuff. Oh well, at least if the problem doesn't get fixed as soon as I'd like, we're all learning more and more.

9th March 2008, 18:15

I'm about to set off home in 15 mins. I've got about a 1 hour drive. Does anyone want me to test anything while I'm on the road? You've got to be quick though... lol

9th March 2008, 20:48

lol, cant remember the sensor name, are the crank sensors? prone to failing, ie the engine is thinking it's reving slower than it is.

9th March 2008, 21:40

Guys, I give up!

I started the car (from cold) and the revs started around 2000rpm, and it didn't seem too happy. I ventured on anyway, and the car was really difficult to drive with the same symptoms. So within a couple of mins from starting her up, I parked and unplugged the IACv, then firmly seated it back in. Started the car up and it seemed OK. It took me about an hour to get home, and the car was completely fine the whole journey. I spent a lot of timing sitting is traffic so it was a real blessing that the problem didn't start up. Do you think this whole fiasco could be down to a dodgy connection?

10th March 2008, 08:12

It's possible, if you intermitantly loosing connection on just one of the coils.

Ross
RCD.

10th March 2008, 09:10

Well I've really gone and messed things up now. Honestly, anything mechanical I touch, I friggin' break.

Thinking that it might be a connection issue, I unplugged the IACv and inspected the connection on the plug from the loom. They were nice and clean, but maybe a little bit open, so they might not be getting a perfect contact with the IACv. I took a pair of nail scissors and pinched them in a little to help the contact. When I put the connection back on, it was really tough to get it on, but I forced it anyway. Went to start the car, and as soon as it started running it would just stall if I didn't give any throttle. Oops

So I took the connection back off only to find that I'd bent some of the connections on the loom part. Bugger! I managed to squeeze them back, but I noticed that the 2nd one (or 3rd depending on which way you are looking at the plug) was a bit mashed beyond scissor repair. Big bugger! Toad = Twat! I've managed to lose a bit of the copper connection on this particular one. (2nd or 3rd) I moved what was left of the copper into the middle so it should make and a connection with the IACv, plugged it back in, and hey presto, car started and idled fine. Hmm, don't know if I got lucky, or perhaps that 2nd or 3rd connection isn't critical?

Ross, you got these wires incorrectly attached didn't you? Do you remember what function the middle ones did?

10th March 2008, 09:52

basically mate the four wires are the ends of 2 coils, i.e. 2 wire for each coil, the ECU sends a signal to each coil individually turning the motor 90deg. then the pulse on the other coil pulls the motor round the next 90deg if that makes sense.

So what state are the wires in at the moment?

10th March 2008, 10:01

So if 1 of the 4 coils is damaged it won't matter as it's backed up by the other, is that what you mean? Although, I can see 4 different colured wires coming out of the plug.

Basically mate, you know how the connections on the plug are "female" and the connections on the IACv are "male" right? Well, on one of the female connections, part of the copper bit has disappeared, so instead of having 2 pieces of copper for "male" part to slide into, there's only one bit left. Does that make sense?

10th March 2008, 10:03

Yeah that makes sense mate, might be a good idea to have a new connector put on, as the way it makes a good connection is by "gripping" the male connector.

What i mean is one coil turns the spindle 90deg, then the second coil the next 90deg, the first coil the next 90deg, the second the next and so on, so if one coil is foobed it wont turn

10th March 2008, 10:15

Ah I see. So I assume it takes both supporting wires to activate the one coil? Hence, all 4 wires are required. Where abouts does the plug go to? Is it a part I can buy from Pug? I remember I went to Pug a few months back when I had an issue with the cable that runs from my alternator to the battery. Anyway, I asked Pug for a new cable, and they told me I had to buy a whole new loom! Can you believe it?!!!

That would be over £300 to replace one single foot of cable. What a joke...

10th March 2008, 10:34

Quote:

Originally Posted by saxodan

driving along and in second and the accelrator just dropped ot the floor, had to pop it out gear.

cable looked fine from the engine but half way down it was seved and not relaesing

garage sorted it out in ten mins

had the same problem driving over christmas accelerator lodged itself to the ground

switched engine off and rolled to a stop on a blind crest.

Fiddled around with the cable pulled the accelerator back up and everything was fine... just needed some wd40

10th March 2008, 11:10

The plugs part of the loom, so you could buy a new loom...or not

We could solder a new plug on there, cut a decent plug from a scrapyard etc, and solder it on

10th March 2008, 11:11

Just to clear up a few point. Alex, you are very incorrect regarding your comments surrounding the IAC valve.

It is around 240 steps from open (high rev) to closed (engine stalls).

When fully open it will pass sufficient air past the throttle butterfly to rev the car to the limiter. 65 steps is around 5500rpm. 20 or 30 steps would *easily* see the redline.

I know this, because I can sit on my laptop in the car, tell it to move to 65 steps and watch the rev counter move to 5500rpm.

If I move the idle valve to around 205 steps when warm, it ticks over at 1000rpm or thereabouts. When I move it to 220, 230, 240 or so the car stalls.

The standard position for the butterfly 'stopper' does not allow sufficient air on its own to hold a tickover, it needs supplemental air from the IAC.

Because these devices are so 'dodgy' most aftermarket ECU companies set the IAC valve to 250 steps permanently in the software and wind open the butterfly to maintain idle in the "old fashioned" way.

We are trying to use the IAC in the 'factory' way without having to resort to just butterfly tickover, but it's such a complete pig-dog to do we are close to defeat. Even in 'closed loop' idle it is fluffy and does what's described here.

Hope this helps

Andy
RCD Performance

10th March 2008, 11:31

Quote:

Originally Posted by RCD-Performance

The plugs part of the loom, so you could buy a new loom...or not

We could solder a new plug on there, cut a decent plug from a scrapyard etc, and solder it on

Nice one. I wouldn't want to turn up at yours with a fooked plug and defeat the main purpose of the visit. Have you got any scrappies round your way?

10th March 2008, 11:33

Quote:

Originally Posted by luthor1

Just to clear up a few point. Alex, you are very incorrect regarding your comments surrounding the IAC valve.

It is around 240 steps from open (high rev) to closed (engine stalls).

When fully open it will pass sufficient air past the throttle butterfly to rev the car to the limiter. 65 steps is around 5500rpm. 20 or 30 steps would *easily* see the redline.

I know this, because I can sit on my laptop in the car, tell it to move to 65 steps and watch the rev counter move to 5500rpm.

If I move the idle valve to around 205 steps when warm, it ticks over at 1000rpm or thereabouts. When I move it to 220, 230, 240 or so the car stalls.

The standard position for the butterfly 'stopper' does not allow sufficient air on its own to hold a tickover, it needs supplemental air from the IAC.

Because these devices are so 'dodgy' most aftermarket ECU companies set the IAC valve to 250 steps permanently in the software and wind open the butterfly to maintain idle in the "old fashioned" way.

We are trying to use the IAC in the 'factory' way without having to resort to just butterfly tickover, but it's such a complete pig-dog to do we are close to defeat. Even in 'closed loop' idle it is fluffy and does what's described here.

Hope this helps

Andy
RCD Performance

Thanks for the great insight Andy!

10th March 2008, 11:57

Quote:

Originally Posted by Toad

Nice one. I wouldn't want to turn up at yours with a fooked plug and defeat the main purpose of the visit. Have you got any scrappies round your way?

I'll see if can get hold of one mate.

10th March 2008, 12:14

Thanks man. I don't understand why you are being so helpfull, but I'm certainly not complaining!!! Thank again.

10th March 2008, 12:49

Your more than welcome mate!

10th March 2008, 16:08

A friend on another forum made an interesting point here. He mentioned that if the ECU was to blame here, it's possible it could be getting incorrect readings from the TDC sensor, which would mean the ECU could be telling the IACv false RPM readings? What do you think? So basically, if the ECU tells the IACv that the engine is revving at 800rpm, but I'm actually at 4000rpm... we could have a possible answer.

One other thing... Where's this TDC sensor?

10th March 2008, 20:13

the "VR" sensor is located where the gearbox joins the engine, infront of the coolant temp sensors down on the front edge of the gearbox bell-housing.

If there was a dodgy signal, you would get many more issues, like the tacho jumping about....

Andy
RCD Performance

10th March 2008, 20:28

OK, nice one for clearing that up.

11th March 2008, 08:40

Guys, I couldn't bare the thought of having to use the 1.4 automatic Polo to get to work this morning, so I used the good ol 106.

From start to finish, it was absolutely spot on. It cold started perfectly and there was never a hint of the revs sticking, or the idle going all funky... Ross, I'm thinking of writing this one off as a dodgy connection with IACv, what do you reckon?

11th March 2008, 10:03

Could possibly be that mate, would account for the irratic behaviour!

If your still heading down thurs i can check the state of the connectors for you and see if the connection of a wire does go when wiggled

Ross

11th March 2008, 11:05

Yeah cool mate. I'm still up for coming down, if it's not problem for you though? You never know, the problem might reoccur in the meantime anyhow.

I'll keep using the car to see if the problem happens again.

11th March 2008, 21:48

No problem at all mate, my number is in my sig, give me a ring in the morning!

Ross

18th March 2008, 23:03

Bad news guys. Very bad news...

After a perfect past couple of days, the car fooked up big time on the way home from work this evening. I'll try to explain in as much detail as possible...

Started her up, and the revs went up to 2k, and slowly started to climb. I turned off the ignition, and tried again - same problem. I checked the IACv connections, and tried again, no dice! On like the 5th attempt, the revs went to normal idle, but every 5 or so seconds, it was if I was bliping the throttle, as the revs would go to 2k and then fall, really odd.

Anyway, I needed to make tracks so I took off hoping for the best. As soon as I got to the slip road to get on the motorway, and I had the opportunity do accelerate over 30mph, the car seemed to start missing really badly. The power kept dropping even though I was on the throttle. While trying to hold a steady speed of 60mph in 5th, every 10 or so seconds, the car would stuter, the exhaust would pop and power would be lost.

I took the car up to around 75mph and it seemed a little happier, but every time I took my foot off the accelerator, the same thing happened basically, the car would lose power, exhaust popped and spluttered and power was immediately lost.

I kept going as the journey on the motorway was around 15 miles, and it was not pleasant I can tell you. Everytime I was light or coming off the throttle I nearly snapped my neck with the way the car was behaving!

BUT, for the last 5 mins of the journey, the problem completely vanished! What the fooooooook!!??!

The fact that I was getting the misfire symptons leads me to think the problem might be coil pack related, but it seemed odd how it seemed to revolve around coming off the throttle and the like. Do you think it could be TPS related after all? Man I'm confused! Please help.

19th March 2008, 07:42

Hi Toad thanks for the PM. I thought i'd reply on here

Get that car down to us, i assume your still heading down next week and we'll get to the bottom fo this if you are wanting some help

19th March 2008, 12:24

Another update...

I didn't have much time on my hands this morning, but I checked over a few things. I wanted to remove the TPS housing, but the awkward location of the screw was too much for my skills. Grrr. I unplugged the wiring to the TPS anyway, and pressed the connections together on the plug so it fitted tighter. I did the same to the IACv plug again too. I took off the coil pack and inspected it for any obvious issues; none found. Sparkies were all fine, they're not that old anyway.

Used the car to get to work this morning and it was absolutely fine! lol! I give up...

19th March 2008, 13:38

i get the feeling your car just doesnt like you

19th March 2008, 13:58

Quote:

Originally Posted by samcook

i get the feeling your car just doesnt like you

Sod...

19th March 2008, 13:59

I agree with you though...

25th August 2008, 20:24

what was the cure to this toad?

27th September 2008, 20:28

Did this problem get resolved?

13th November 2012, 10:46

Hi guys sorry to bump such an ancient thread but does anyone no what the soloution to this is, as i have exactly the same problem so far i have, changed map sensor, chaned green temp sensor, clean icv sprayed carb cleaner in and around the throttle body itself tried red x etc yet still the problem persists.

All help and advice is greatly appreciated
Thanks
Tom

13th November 2012, 22:04

Bump nobody no?

15th November 2012, 22:29

ttt someone must no its doing my headin