Right at the top of the engine you will find the carb immediatley to the right on the carb you will see a flat head screw this will adjust your idle , helps to have a second person on this.
Is it a stick shift?
You may have to clean or replace you Idle Air Control (IAC) valve. Mine did the same thing, but after I cleaned it, I realized that it idled too low, so now I have to replace. Be forwarned... you will most likely have to order the part (it cost about $43.00) or you can get one from a junkyard if you trust that. Hope this helps.
How high is your idle? idle should be 800rpm good oil pressure is obtained at this idle
Was there any recent work done to the car? When did the idle problem start? Does the idle get worst when you turn on the AC? Answer these questions and then I may help.
auto or stick shift
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What is the right order location for relays on a 1987 420SEL Mercedes-Benz?
The idle speed is set at the factory and is NOT adjustable.
Depending on which engine is in, I know that it's on top-right part of the engine on the 8V model.
the idle tensioner and or the distributor.
all idle speeds arfe controlled by the computer and are not adjustable.