It is not uncommon for the idle air compensator to get stuck in one position, resulting in the engine idle speed (rpm) being too high or too low. Replacement of the failed compensator may be necessary to correct this concern.
Car Problem Reports
Mercedes-Benz 420SEL Stuck Idle Air Compensator May Cause Too High/Too Low RPM
Mercedes-Benz 420SEL Problem
Average Mileage: 128,283 mi (58,000 mi - 198,566 mi)
when engine is running and shift to drive gear and pressthe acceleration the engine shut off
Visitor, 1991 Mercedes-Benz 420SEL, 198,566 mi
Sometimes idles to high. More often than not. Hard to crank after sitting awhile.
idles about 2000 rpm on hot engin in park and 900 rpm in dr