Mercedes Benz repair: 190e idle surging from 750 to 1500rpm, vacuum leak, line leak

Question
Greetings,

I have a 1987 Mercedes 190e 2.3 automatic, 201-028 body and 102.985 engine.

Many times while idling in neutral, the RPM's surges from 750 to about 1500 RPM's within a few seconds.  There also seems to be a whistling noise coming from the engine.  It seems like the car is trying to find the right idle speed.  

Can you give me an idea about things to check to diagnose this problem.

Thanks for your response,
Jim

Answer
There is a vacuum leak somewhere in the system. The idle changes according to how much air is getting into the system. You could have a bad manifold gasket or a simple vaccum line leak somewhere on the intake. Get some WD40 and spray it around the intake manifold and see if the idle changes, if it does then there is a leak. It should be fairly easy to pinpoint.