on a peugot 206 why do revs increase on their own?

Could be the idle speed control valve, also called the stepper motor. Replaced one last week on on a 206, the revs were staying at a constant high. It was an older model and if its the same the part was quite expensive new and gold dust on a scrapyard. Should be cylindrical and located on the left hand side of the throttle body, 2 bolt fitting and has a plunger inside it. With limited information i can only guess.

Russ
September 2012