Hi all, I have a 1992 400E that has a strange running problem that keeps gradually getting worse. When the car is started cold, it runs fine, and drives fine... for about 10 minutes. Then it starts misfiring and running rough/bogging down, and more recently backfiring in the engine compartment. After about 5 minutes of this, it clears up and then runs fine for the rest of the day. The last thing I did was clean the MAF sensor, but that didn't seem to make a difference. This seems to be an engine temperature related problem. Spark plugs are recent, wiring harness has been done, fuel injectors have been professionally cleaned. No issues with ASR, no error lights on the dash, though I don't have a Check Engine light on the car.

Anybody have any ideas?

I have a 92 400E. Had exactly same problem until it stopped recovering and running normally for the duration. Spent over 1000.00 and at the shop nearly a month ( a certified Mercedes Benz shop by the way) and the only thing that they accomplished was to destroy the intake hoses and scratch the door jam when they took out the rear seat. Friend recommended a great shop. 10 minutes...better computer diagnostic capabilities and the answer. Bad spark plug wires. Fixed the problem. Be aware that the wire set from Phil at Fastlane has a one coil wire that doesn't fit the car. It is too short. Good luck.

Thank you. You know, those havent been replaced, and they look pretty old. I will try that.

Get the codes . That may help send the diagnosis in the right direction.

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A Dalton

You might consider saving yourself a lot of work and ordering just the resistor boots that go over the plugs. You can simply unscrew the old ones and install the new boots. The wires are solid core and not like the plug wires on domestic cars. They seem to last a long time.

Silicone spray will facilitate reseating the wires at both ends.

If you order the wire from MB--by the meter--I can assure you that you're in for quite a job, because you'll have to use a special tool to crimp the metal end caps. I replaced mine, but then realized that they probably didn't need it.

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1993 400E, 256,000 miles (totaled)
1994 E420, 200,000+ miles
1995 E420, 201,000 miles