A 380sl I've been restoring had a surging idle. So I had Programma rebuild the idle control unit, which cured the surging.

However, the car is now idling in gear at around 1000-1100 RPM's, rather than in the normal 600-700 range, and tweaking the potentiometer on the unit doesn't seem to do very much.

So I was wondering if anyone here could tell me what that potentiometer is supposed to do, if not somehow increase and decrease the idle.

Thanks very much in advance.

Could be a vacuum leak somewhere.
Or your ERG valve might be gunked up.

Spraying the engine with brake fluid didn't affect the idle at all, and AFAIK the car doesn't have an EGR.