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I was driving the car today, and then all of a sudden i hear something (maybe not related to this problem) a sound like a pop, then all of a sudden between 2k and 3k rpm the car is jolting and really lumpy, when driving, then when i pulled over and lifted the bonet to check it out, i feather the throttle at around 2 k, just leavin my foot on the pedal and its reving by itself! its also backfiring when doing this. Also the header tank keeps blowing its load? i loosened the cap to see if there was a problem, then tighened it and it keeps opening the release valve. Then on the drive home the car is fine for a wile, then it starts jolting (the jolting is asif im floring it then letin off then flooring it again) now it has stopped again but i have no idea wat it is, i think its electrical. HELP ME PLEASE!

UPDATE: My dad took the distributor cap off, and there is this like yellow dusty crap in there, and where the shaft is, theres like chunks of this yellow plasticy stuff? its like coming from behind the plate, where the shaft comes out. Any ideas?

id blast it with some wd40

"yellow stuff" could be fried electrodeso the insde??

sounds bogus! I've had dizzy cap troubles before with lots of dust and crud... but nothing plasticky... and nothing yellow!

wiggle the rotor arm off (dont worry it's "keyed" so will only go back on one way) and remove the moisture cap for a better look?

luckily i recently found out the actual dizzy itself comes out quite easy (couple of bolts and a tug*), just remember to put a dab of tippex on the unit and the body to preserve the timing

*might have to remove the cam cover & oil baffle first, but nothing more than that


EDIT: the header tank / pressure valve going like that suggests something less electrodey though - perhaps it's overheating badly but your temp guage isn't showing it up for some reason? lost coolant, and the rest is turning to steam causing the overpressure?
at the outside, it revving itself when you're trying to keep a steady rpm *could* (could) be the temp sensor(s) or lambda?
(someone help here, ive run out of straws)

Thanx for the reply's, my dad recons its an air lock in the cooling system causing the pressure valve to go off when the car has stopped running. Im gonna try to bleed the system. Any other ideas?