95 E320 Stumbling Idle - PeachParts Mercedes-Benz Forum

#1 08-31-2002, 10:48 PM

Hi all,

After reading through 7 plus pages of archives on this problem I really didn't see anything that would help me, so here it goes.

For the last few weeks my 95 E320 w/155k miles sporadically stumbles at idle, only when in reverse or drive. Engine temps. nor a/c on or off matters. When I come to a stop it will (sometimes) fall to around 500rpm for a second, then go back up around 800. It has never stalled out.

There are no codes using the built in LED or with pins 8 and 14. (I have a code reader thanks to Arthur Dalton). The cruise works perfect, gas mileage is still 21 to 24mpg around town, it goes like hell, nice and smooth. No other problems with the car.

Here's what I've tried so far:

1. Plugged the vacuum line going to the EGR - no help
2. Thoroughly cleaned the throttle linkage and lubed - no help
3. Repeatedly checked for vacuum leaks, none noticed

5k miles ago (at the 150k service I did) I replaced the plugs, coil boots, coil to plug wires, fuel filter, and every fluid in it.

Any ideas guys???

Dale

suginami · #2 09-01-2002, 12:29 AM

It sounds to me like a symptom of a bad engine wiring harness.

They were bad on all MB's with the M104 engine from 93-95.

Do you know if yours has been replaced?

Do a search on engine wiring harness, and you'll be up all night reading.

suginami · #3 09-01-2002, 12:32 AM

I just thought that it might also be a bad coil wire.

You have 3 coil wires and 3 spark plug wires that pig-tail to the next cylinder. Each coil wire is responsible for two cylinders.

The resistance in MB wires is in the boot or end of the wire, just like Porsche and VW's.

It is usually the boot that goes bad, not the wire, and it is cheap to replace the boots - a couple of dollars for the three.

#4 09-01-2002, 11:24 AM

I replaced the coil boots about 6 months ago. I'm not sure if my wiring harness was replaced or not, I do know that I haven't been able to find any sign of deterioration with it or cracked insulation.

suginami · #5 09-01-2002, 01:23 PM

Are you sure you know how to check?

If the wiring harness has been replaced, then you're in luck.

If it's the original harness, I am 100% sure that the insulation has turned white-ish in color and is either flaking off, or has completely turned to powder, exposing the copper wires.

I took a utility knife and carefully slit open the black fabric covering the wiring harness on the firewall behind the engine. The insulation on the wires looked like new, it was intact, and the insulation on the wires had many different colors like it should. I visited the dealer and had a vehicle master inquiry printed out, and it showed me that it was, in fact, replaced as a "good-will" warranty in 2001 at 107,000 miles by the previous owner.

If you're unsure of checking it yourself, take it to a good Mercedes mechanic or the dealer and have it checked out. You may try and plead your case and getting it replaced as a good-will warranty. They might cover the cost of the harness, and you'll have to pay for the labor.

FWIW, the harness will run you about $550, and many techs have posted that it'll take 2.5-3.0 hours to replace.

suginami · #6 09-01-2002, 01:27 PM

I noticed that you are in Atlanta.

How far are you from Sugarhill?

Benzmac's (Donnie's) and Bill Wood's shop, MB Autowerks, might be a good place to have your car looked at if it's not too far.

http://www.mbautowerks.com/

#7 09-01-2002, 01:58 PM

Paul,

Sugar Hill is not too far from me, maybe about 40 minutes (that is very traffic dependent). I'll go out right now and look at the harness like you just described and see what I've got, then report back in a few minutes.

Thanks

Arthur Dalton · #8 09-01-2002, 02:04 PM

JF
I don't know if I had mentioned it or not when we off line a while back, but there was an EGR TSB on that car for sticking EGR valve.. That could very well fit you symtoms at idle..
I can send that info your way, if needed, for new part # comparison.
Arthur

suginami · #9 09-01-2002, 02:17 PM

I wonder if a sticking EGR valve would've tripped the CE light...?

Arthur Dalton · #10 09-01-2002, 02:27 PM

An intermittant one won't cuz it has to do it in sucession
or else the computer erases the memory after so many drive cycles if it does not repeat..so the code does not trip..

As I think about it , it prolly isn't egr related as he has BBed the line from the SOV.....

#11 09-01-2002, 02:31 PM

Arthur and Paul,

I peeled back the insulation on the engine wiring harness on the firewall above the engine and the wires all looked fine. They were flexible, no insulation showing so I'm guessing that it's been replaced at some point.

BUT........I just rechecked the codes and it came up with a code 40 out of socket 8. According to my PM disc this indicates a problem with the Trans. overload switch. Do you think the stumbling idle may be related to this code?

suginami · #12 09-01-2002, 02:55 PM

"They were flexible, no insulation showing so I'm guessing that it's been replaced at some point"

It's the other way around. The insulation should be showing. In other words, the wires should like as you'd expect them to. You should see white, green, red, black, etc. If you saw the insulation flaking off and you saw the bare copper wires showing underneath, then you're in trouble.

In any event, when you're done, wrap up the area that you cut open with black electrical tape.

#13 09-01-2002, 03:06 PM

Okay Paul, you got me. I did mean it the other way around. I think I'll blame it on too much beer last night!!!

#14 09-01-2002, 03:30 PM

gents, before we go chasing a code 40 I think I know what caused it. I just rembered that while looking for vacuum leaks yesterday, with the engine running, I removed the vacuum line located aft of the oil dipstick which goes down to the trans. vacuum modulator. I bet that is what caused the code 40 which has nothing to do with my stumbling idle.

Just to add a little more information, after the initial stumble it will idle perfectly. That is until I go another 30 feet and stop (Atlanta traffic) and then it will do it again.

Arthur Dalton · #15 09-01-2002, 03:46 PM

Does it stumble as you come to the stop or at the start of accelleration?