'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.