I have 120K on a 93 300E 3.2L. The engine has no problems at all and runs strong. I have noticed that when I am waiting at a stop sign/ red light, the RPM's drop from 1000 to 500 and the car ascts as though it will stall. It still has not stalled however it shutters and acts as such.

I found that whn I drop it into Neutral though, the RPM's stay right at 1000 and there is no hesitation at all.

Someone suggested a "Idle Control Motor". Is this accurate?

Any suggestions?

Thanks,
Jeff

Your car has a throttle actuator, and it could be causing your problem.

Another item could be the mass air meter.

You should also check for vacum leaks. There is a plastic vauum line at the front of the engine going to the Air Pump switch-over-valve. They commonly crack from heat and this can cause a rough idle.

Have you replaced the spark plugs and the three resistor boots under each coil?

__________________
Paul S.

2001 E430, Bourdeaux Red, Oyster interior.
79,200 miles.

1973 280SE 4.5, 170,000 miles. 568 Signal Red, Black MB Tex. "The Red Baron".

I did replace the plugs and boots. Are there any other vaccum lines I should focus on? How can I test for the airflow meter you are referring to?

Yes. Check the plastic vacuum line that I referenced in my earlier reply. That is the most common place for a vacuum leak.

I had a similar problem, but the idle went up and down like crazy. The car was not driveable. The vacuum leak was at the intake manifold gasket, but I believe my situation was very unusual.

You can test a mass air meter if you have a scope, but I've never done it.

I gather from the techs that it takes more time to test them than they're worth.

Instead, most shops keep a good mass air meter on hand and switch it out to see if it makes a difference.

You can replace your mass air meter with a phillips head screwdriver and about 15-20 minutes. The problem is that you don't have a known good spare MAM to swap with yours, and they cost a couple hundred dollars. Most shops don't allow return on electrical items, so tread cautiously on this.

The throttle actuator costs about $1,200 by the way, so keep your fingers crossed.

__________________
Paul S.

2001 E430, Bourdeaux Red, Oyster interior.
79,200 miles.

1973 280SE 4.5, 170,000 miles. 568 Signal Red, Black MB Tex. "The Red Baron".