if there is soem oil and muck stuck round it, it my swell up (the metal that is) just enough to make it stick, but im thinking of a cossie one that opens ans closes a small valve, thinking about it , i think the mondeo ones are a servo motor..... but im not sure, if you can get to it, get it off and give it a good clean with some carb cleaner, youll see lots of black gunk come out from it i reckon...


the other option is a ar leak on the inlet manifold, this will make it rev fast at idle aswell...