Check out the air filter. I have 95 E320 and had the same problem in idol. Well at last I found that the air filter was the main culprit.
Secondly disconnect your car MAF from the air filter. Start the engine and ask someone to sit on the wheel and rev the engine to 2000 RPM. Slowly and steadily spray any carburetor cleaner or a brake cleaner inside the MAF window. This will thoroughly clear any dust accumulated on the MAF sensor and will also clear the throttle body. You will be amazed to see the smoothness of the engine. Don’t spray too much. While you are spraying the carburetor cleaner inside the MAP the car engine will sputter, don’t worry nothing will happen. Where ever you feel that the engine is dying stop the spray and then again start the spaying, till that time you feel that the idol condition has improved.
Do let us know about the progress.