Hello, my 95 E420 drives well most of the time but occasionally at stoplights the idle speed jumps up and down rapidly from about 350rpm to 1000rpm. It does this whether the ventilation system is on or off. It stops if I put it in neutral and tap the gas. So far the problem is intermittent but I'm worried as my car goes out of warranty soon. Thanks for anything you can come up with. Beth

There are many systems working in harmony to develop a smooth reliable idle. The systems are numerous. Since you are most likely not a tech who is going to be doing the repairs yourself, I will try to reply to you as if you will be speaking to your service advisor or technician about the problems.

The idle surge should cause a “check engine” light to illuminate on the dash panel of your car. If so you are in luck! The repair technician can retrieve the code stored in the Diagnostic Module. After retrieval, the technician should perform diagnostic work to find the exact cause of your complaint. There could be many codes in a series, but only usually only one caused the complaint and the “check engine” light illumination.

Some causes that I have seen are as follows: 1. The self-adaptation is at its limit. This means the engine is running too rich or lean. IE air leaks or faulty sensors. 2. The engine wiring harness is cracked. See the bulletin board for more details on this. 3. A broken throttle return spring 4. A faulty throttle actuator

I hope I have helped!

Benzmac

I also have this same issue on my '94 e420. I have had the codes pulled and the verdict was the "Idle speed slider(Actuator)" was faulty. $1200.00 from MB, YOW! Anybody have a handle on rebuilt part? I am in Denver, CO.

BETH,
YOUR CAR IS EQUIPTED WITH AN "ELETRONIC"
ACCELERATOR. SOMETHING IN THE FUEL MANAGEMENT
SYSTEM IS SENDING INFORMATION CAUSING THIS
ERATTIC IDLE SPEED. BEFORE YOUR WARRANTY EXPIRES HAVE YOUR DEALER CHECK IT OVER.
PLEASE ALSO READ BENZMAC'S ARTICLE;
"CHECK YOUR ENGINES WIRING HARNESS".