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intermittant rough idle on start 1994 E420

4559 Views 5 Replies 4 Participants Last post by  redwood
Hello -

Have been browsing the wonderful articles here and must say you guys know your stuff!

I am making this post to take one last stab at solving this cars problems once and for all.

Problem - Intermittantly, more so during cold months (SF Bay Area cold) after car has been sitting overnight. On start engine will run on 6 cylinders for ~2 mins then smooth out. Also notice cold stumble on first cold start after overnight sit or at work (could be emissions unrelated since it has CA emissions on it)

It never does it more than 2 minutes so no shop can take any readings on anything no matter how long I leave it with them.

It has been doing this for about 2 years and among other things I will get into later, I am still baffled for a solution.

What has been attempted over the years.

o When I purchased the car 3 years ago it was missing consistently and it never went away.
solution - new caps and rotors
seemed to tame it for a while

Remember, this is intermittant. IE - it will do it once then wont re-appear for 2 weeks sometimes.

Into an independent repair shop MB & BMW specialists -- they suspect leaking down injector -- they replace 2 of them. It goes away for a while.

I replace spark plugs multiple times. No change.

I move to Seattle (cold and damp there) it is doing it more regularly. Take it into dealer, they relive me of $400.00 and replace the caps and rotors again then bring it to me missing and stinking up the shop. I demand my money back and get to leave with new parts since they tossed the old ones. They mention leak down problem with the injectors as well.

I dont hold MB dealers in high esteem at all..

I move back to California and the problem continues. I take it to my non-mb spec. mechanic and send out all of the fuel injectors for rebuild. I never could find a price less than $150.00/ea and there are 8 of them. Rebuild cost $340.00
Had them re-installed, problem came back again after a while.

I find a nice set of plug wires for less than $600.00 and install them myself (what a pain!!! took me 4 hours)

Year goes by with problem persisting intermittantly.

Then my check engine comes on (it wasnt missing when it came on) and I wasnt there since I loaned the car to my brother.

Took it to my non-MB specialist mechanic - He finds 2 codes. He suggests replacing the computer but wants to trace the wiring down first.

code 19 - Fuel injectors open/short circuit or self adaptation in LH-SFI control module "n3/1" at limit
code 21 - Purge switchover valve open/short circuit

He traces the fuel injector wiring presumably and finds no problems with power to the injectors themselves. He makes no mention as to the quality of this wiring but says he tested voltage to each injector by hand.

He ends up resetting the light and it has been off ever since.

Start it this AM and it is up to it's old tricks again.

I have read some articles about the wiring harness on this model causing all sorts of headaches and wonder if that could be the case or if the injector re-build was a failure and I should just get them all replaced with different ones.

I am reluctant to throw money at it if it wont solve the problem. I am probably North of $1K for this already.

Other problems which you guys may comment on separately include.

Why does it take 3 trips back to the tire place (no matter who it is) to get the tires and/or alighnment done properly? This blows my mind. I have switched tire brands several times and even had to go back to an "alignment expert" twice to have it looked at. I even took it to MB once thinking I would get a better balance. The morons left the original weights on and counter balanced the tires. Nice!

It is getting right around the mileage where it is going to need water pump/alternator and god knows what else.

I am considering dumping it for a new Infiniti G35. I am torn, none of the other cars I have looked at have the same ride quality and fewer still have the nice smooth power this car has when it is running properly.

but yet I am coming to the conclusion that, really no matter how much you dump into it will be a pittance to dropping $30K for a new car to replace it.

btw, on the NHTSA web site, I am the one that submitted the complaint about the rear link pin breaking and destroying my rear suspension and almost killing me.

Thoughts, ideas... long message, I know but this has been plaguing me for a long time and I am one of those guys that believes a Mercedes should be a trouble-free motoring experience...

Thanks for your time
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I am going to share this piece of information I have found while trying to diagnose a similar problem in my car. The tempreture sensor located on the top intake pipe for the raiator (it has a 4 pin xlr type connector on it) when it goes bad it send incorrect temp. information to your computer. ie it will run richer on idle to compensate. This part can be purchased at the dealer for 23 dollars. It is a small price to pay. Try this as it has worked for me. I was told all the same BS you got fed re: injectors fuel pumps etc. I went over everything in my fuel system with MB at the dealer. I have a friend there so no money loss. It took about 3 trips to find the problem but all fuel system is working fine. Let me know if this helps...
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