I have a 97 E420. The car run fine except for one thing. When the car is in Park or Neutral it idles at 700 rpm. When I put it into Drive the idle dropes to around 400~500 rpm. The air conditioning can be on or off and the computer has no errors. The dealer mentioned to look for a vacuum leak. Is there a vacuum line from the transmission to the engine to tell the engine when the tranmission is in gear (Drive)?

I can't find anything within the service CD, its not the easest to use.

 

i have the same problem!

 

We have different cars but that is normal idle speed with mine.