Your idle speed is controlled by the EA/CC/ISC Module (Electronic Accelerator/Cruise Cntrl/Idle Speed Cntrl). The common name, though, is throttle actuator.

If your actuator is actually bad, get your checkbook or credit card ready, because it is about a $1,000 part.

Parts Shop sells it for about $961.00.

Good luck.

__________________
Paul S.

2001 E430, Bourdeaux Red, Oyster interior.
79,200 miles.

1973 280SE 4.5, 170,000 miles. 568 Signal Red, Black MB Tex. "The Red Baron".