Sometimes my 400E idles at less than 500 RPM at a stop light. Most noticable with A/C running (warm weather).
Finally noticed this problem accompanies the cruise control not working! Shut off ignition and re-start, no problem!
This morning I stomped on the gas to enter traffic and, no cruise and rough <500 RPM idle!
Now I think the belt tension is too loose and the A/C pump is slipping under hard acceleration and shutting off one of the computers.

Any comments?

Norm

I searched threads with idle problems trying to identify my idle problem, which was different than yours.

What I found over and over again is that the throttle actuator is a common failure part. When the throttle actuator goes out, the cruise control goes with it. The fact that your cruise control is not working along with a bad idle is not a good sign.

Hopefully it's something else.

This would not be good news as the throttle actuator is about $1,000.

__________________
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".

Okay, I have replaced the spark plugs, spark plug wires, o2 sensor, distributor cap & rotor, and fuel pressure regulator. Last night, while checking the threads again. I came upon something about the 300TD fuel injection thread. It specified about the idle valve control. Now, I read about this before on another thread and someone said there isn't one for the 400E but, last week or so. I heard a tick from a device behind the horn in front of the Ignition control module. It has two hoses and a electronic connector on top. One hose on the side says nothing and the other hose is imprinted,"hot" It was ticking like a time bomb while, I pulled up in the garage. I did not want to touch it since, I did not know what it was. The ticking stopped after, I restarted the engine. I did not know what was until, last night when the thread about the 300E described the same component. So, I took out some contact cleaner spray and sprayed it into the hose where the ticking(hose not labelled "hot") was as, well as the idle control valve internally. Then, I sprayed a little WD-40 becasue, the 300TD F.I. thread mentioned to do that. Now, my car idles smooth as silk. So, you might want to do this first. It takes about 3 mins. So, I am closing out this thread about half a year later finally!

Have you tested your cruise control yet? I'm curious to know if it working now too.

It's always been working and yes, I checked it again today. No ABS light. It is not the fuses in the computer box. I checked those already about 5 months ago.

I still have to do the wiring harness because, I checked the insulation and the insulation looks similar to the pictures of the corroding wiring harness pictures that were previously posted.

I checked the list of DTC codes and if the wiring harness was a problem. Wouldn't it trip code 19 for my car? Code 19=Fuel injectors open/short or self-adaption in LH-SFI control unit (N3/1) at limit. That lead me to believe it was something else.
The wiring harness consists of fuel injector wiring and temp wiring. Correct me if I am wrong. The computer with the fuses has the Cruise Control , ABS, and something else. i forgot. That is what I was lead to believe from the past posts on the forum.

Supplement:
Please do not use cleaners such as, carb or brake cleaner or anything else that may be harsh to clean this valve. It may cause inoperation or a leak of your idle valve. Use electric contact cleaner that is safe for plastics and circuitry(does not cause shorting when applied). Harsh cleaners will detoriate any plastics or rubber components that may damage the internals of the valve.

Also, do not apply WD-40. It may cause further clogging of the valve and future problems later.

I have cleaned out the valve again without the WD-40 due, to a slight miss but, cleaned it out again without the WD-40 this time. It has been good for a week so far without any missing whatsoever. Make sure you clean out both side of the valve where the inlet/outlet are.