i mentiond a few times my car juddering when crusing at 30mph in 4th gear for example, and car revving it self slightly and it making a "vum vum" noise as if its revving but the idle not moveing...then sometimes when i pres the cluch down the engine just cuts out for no reason... i thought it was the oxygen sensor had the changed and i thought it was sorted as it ran ok but a day later problem is back, took it back they gave me a new idle control valve... few days later its still doing it. They checked for a vacume leak but thats ok...recently had a full service...still doing it any ideas?