Hello Everyone and Happy Labor Day Weekend,

I have a 1995 E420 with 150K. I have it serviced professionally, and everything is up to date.

However, yesterday, the car experienced a very unusual engine start, and I would like to see if others have had the same, unusual experience.

Here is the sequence of events:
1) I energize the starter with the ignition key.
2) The starter turns over the engine, and it starts to run at <500 RPM.
3) After about 3 seconds, the engine speed suddenly climbs to >1500 RPM for another 2 to 3 seconds. Nothing is near the throttle....
4) Engine returns to normal idle speed.
5) Engine (and drivetrain) behaves normal thereafter.

The behavior is now continuous.

Please advise.

Lowell C.

Hmmmmm ? Check the engine wire loom....do a wriggle test...but gently !

MAF can cause strange idle problems. Throttle Actuator too.

Any codes ? Especially any Lean Fuel codes.
Check the long term fuel trims.( LTFT ) Short Term Fuel Trim ( STFT.) should be under 7% and changing/ranging at idle.

I've had the exact thing happen to me about nine months ago. I'm not sure what caused it, but it was raining at the time and prior to my starting the engine, I think my wife went through some standing water. I considered that perhaps water in the neutral safety switch was the problem.

It has happened a few times since, but no codes and it goes back to a normal idle after it does it. If you find out what's causing yours, please let us know. My upper and lower engine wiring harness and ETA have been replaced. I think the PO also replaced the ignition control unit and hot wire air flow sensor as well. This model seems to do some unexplained things at times.

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