'92 400E Idle problem
 

My car has 97,000 miles on it.I replaced rotor, cap, spark plugs, and oil change about 5 weeks ago. I have been experiencing a occasional idle problem in which, the car just vibrates. I cannot pinpoint the vibration. It is getting worse though and the car starts shaking at signal lights or while in park. This problem occured about 2wees ago and I just changed out the trans filter and fluid tonight. I checked the level. It is not overfull or underfilled while, the car is idling. The check engine light went on once but, soon disappeared after restarting the car. I checked the red led but, no flashes from the diagnositc. Check engine light only appeared for a minute then, disappeared. I am wondering if this could be a oxygen sensor problem but, it happens now when I drive the car for a minute. Before, it was only after driving for awhile. Anyone else with this problem before?

I don't have an answer but would love to hear if anyone has a fix for this. Mine has ALWAYS vibrated at idle, in drive, in warm weather. When I took it to the dealer when it had 25,000 miles, they said "They all do that" and attributed it to the V8. It now has 113,000 miles and is doing it just like it did 6 years ago.

Mine does NOT do this in cool weather. I have a new fuel pressure regulator, new rotors/caps, and spark plugs. New motor mounts helped a little but it's still noticable and annoying.

Great place to start is to track down some BG 44K to clean up injectors/combustion chambers/valves. Makes Techron look worthless. Also, replace your trans mount.

Those things done, let us know, and good luck!

FWIW, an M119 does NOT do that-when mine has fresh caps & rotors, the only way to tell its idling is to look at the tach:)

also if you used titanium spark plugs, go back to copper. My 260E did the same thing, but when I changed back to copper the problem was gone.

Matt

I called BG and then a local rep called me. He siad he could not sell it to me due, to lack of wholesale license. He referred me to Goodyear. Went there and they do not sell the BG44K itself alone. It comes in a pack of three which consists of the BG44K, intake manifold cleaner(special tool needed which, is not included either), and something else. It sold for $90. I don't think it is worth that much if, I am only using one of the three bottles.

Will try some fuel injection cleaner from Lubro Moly. I tried Techron and agree. It doesn't seem to do much if, anything at all.

The plugs are Bosch Super and are copper

As for the tach moving. I don't see it moving but, the vibration happens too fast or I just see the tailend of the tach moving. It moves but, ever so slightly.

Also, put some carb cleaner around the butterfly plate to, see if it got kind of dirty and resolve the problem. It did not do anything.

However, now it is setting off my check engine light occasionally. I think it is 17 short beeps. Is it code 17? Does anyone what this code means?

TIA

Maybe you can try Pennzoil fuel system cleaner, it cured the rough idle problem on my 400E.

I had experienced the same problem on my 92 400E, I also couldn't find BG 44K that Michael recommended, I then used Pennzoil fuel sytem cleaner instead, the rough idle problem was gone right after an Italian tuneup.

For details, you can search the thread post by me a couple of months ago.

Have you checked the wiring harness(es) on the car? Your model is notorious for that problem.

Setting the CE light off sounds like an emissions fault. Could be an O2 sensor. Not sure if the decaying harness would set off the CE light, but I wouldn't rule it out, either.

Often, warm weather vibrations are attributed to the AC compressor running, and the additional load it places on the engine. This causes the idle to feel a little different than it did during the cooler weather.

I was under the impression that the wiring harnesses were bad only from 1993-1995, and only on all M104 engines - on the C, E, and S classes - on the 2.8 and 3.2 liter engines.

The wiring harnesses on the 1990-1992 3.0 liter M104 300CE's were fine.

While there might be wiring harness issues with some 400E's, it is not systemic to the model, and not due to bad wiring insulation, but maybe chafing of the wires.

Thanks to all for helpful ideas!
Oddly, my idle problem seems to have, at least temporarily, gotten better, now that Omaha has hit 91 degrees F today ...

Now I'm trying to figure out why my 15A aux fan fuse keeps blowing...

Will try the Pennzoil product at some point -- have tried Techron and BG 44K without lasting effects.

I remember reading somewhere that the M119 W124 equipped cars are also wiring harness defective. I could be wrong...

Well, my trouble codes are coming in 3s now. I have a code 2,15, and 17. I will change out the o2 sensor b/c of the code 2. I think the other two codes are due to the o2 sensor.

I bought some Lubro Moly Venti Sauber and Fuel Injection cleaner. Will try that out also.

Where is this engine harness that everyone is talking about on a 400e?

The upper wiring harness runs along the top of the engine and can be seen by removing the air box. And yes, some of the 400e's do indeed suffer from the wiring harness problem. Mine was bad and I ordered the harness from PartsShop and installed it myself. You can check your harness yourself by using a double edge razor blade to make a small slit in the outer harness cover to peer inside and inspect the inner wiring insulation. When you look inside, you'll know if your harness is bad. Be extremely careful when doing the inspection so as not to disturb the inner wiring in case the insulation is breaking down.

Same problem on a 1992 400E.
 

It was the wiring harness. Happened while looking at car to purchase. In shorting out, it fried the controller which had to be replaced. I would definitely check the harness before you damage something expensive, if it hasn't been replaced.

Good luck.

injector cleaner
 

have not tried BG product, but do use Redline Si-1 on a regular basis in my own & cust. cars. can honestly say i've seen results.

'92 400E irratic idle
 

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.

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.