This is actually a common problem on this car. clean the IDLE air control valve with carb cleaner. Its located under the air filter assy. The problem is that the Idle control valve sticks.
I have successfully cleaned them in the past but sometimes they just need to be replaced.

Before you change any parts look in your owners manual and note your milage and see what is needed for your maintance is due also look at engine while running and listen for hissing noises could just be a vac umm leak let in run for a while some vac switches turn on and off even at idel hope this gets you in the ball park Thunderboltz

It could be the OVP Relay that need to be replaced. The new part# is 0005406745. Search on benzworld.org and you can find more info

Sounds like the fuel distibutor. Wear heavy duty gloves to avoid shock. Start the car, pull each plug wire to see which one "DOES NOT change the idle". That would be the problem cyclinder. Turn the car off. First check spark by leaving the plug installed and place a different plug on the wire. Start the car and look for spark. If there is spark then you go to check fuel. Turn the car off, take the plug off the wire and replace the wire to the head. Start the car and loosen the fuel line from the cyclinder in question from the fuel distributor which is under the air filter housing. No fuel flow mean the distributer is bad. If there is a small leak but no flow then it may need cyclinder in questions fuel injector. Good luck

You need a major tune up. Buy the tune up kit and install them.