I've been suffering with this problem for months now. Finally the check engine light came on which hopefully will shed some light on the problem.

Initial problem - no CEL:

- Engine usually runs smooth at cold idle. But not for long - maybe a minute or so.
- When at idle engine will alternate between running smooth and then stumbling and slowing down. Seems like the ECU is trying to keep it from stalling. Whole car will tremble.
- Lower RPM has limited power/torque. Once you get to 3000 RPM or so it pulls much better.
+ I replaced all plugs (not coils) and problem seemed better for a few days. My wife was driving it so I'm not totally sure.

Then recently:

- At highway cruise engine will surge rhythmically. Not always, and not strongly. More of a gentle rocking motion.

And most recently:

- Check engine light came on. I got 5 (EGR) and 8 (coolant temp sensor open circuit). I cleared both codes.

What I have done:

+ I tried disconnectig the EGR vacuum line altogether (and didn't cap it if that matters). Didn't seem to make a difference one way or the other.

>>>> While inspecting the vacuum lines I broke the plastic one in front of the engine that runs to the switch that controls the air pump and EGR - it was very brittle but I don't think it was already broken. I capped it. Now the engine always runs rough at idle but at a consistent speed and I can now also hear it in the exhaust note . Power seems to be back above 2000. Lots of it and makes me remember why I used to like this car.

+ EGR has a dot on top of it so probably it was replaced with the new type at some point.

+ Wiring harness has been replaced before I got car and it looks in excellent shape.

+ I cleaned the MAF and another sensor farther down the manifold with electrical contact cleaner. No difference.

I will be repairing the vacuum line ASAP.

I am STUMPED.

Thanks


E320 1995 176000 miles. One of the later in the year ones.

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1995 E320 with 175000 miles and completely failing original Mercedes paint.

The ECT ( engine coolant temperature ) sensor is VERY crucial to the overall performance of the engine.
You should address this issue before you go any further.

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2007 C 230 Sport.

Thanks, I'll check that. Where is the sensor located? How do I test it? I've searched the forums and can't find a reference.

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1995 E320 with 175000 miles and completely failing original Mercedes paint.

How many miles on the car? How old is the O2 sensor? After replacing the MAF, plugs/wires/coil connectors on my '93 it ran pretty good but still had a lumpy, hunting idle. No codes though. Replacing the 110K mile/13 year old O2 sensor made it perfect. They can be bad enough to affect running without setting a code. Now it idles so smooth I can barely tell the engine is running. I don't know of any way to diagnose other than replacing, unfortunately. The sensor is $100+, but at least it's easy to install.

- JimY

If you need a new O2 sensor, you can save yourself $60: Buy a Bosch sensor for a V8 Ford, cut off the Ford connector, and solder your MB connector in place of it. Presto... $40 MB O2 sensor.

jp

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Jeff Pierce

Current Vehicles:
'92 Mercedes 190E/2.3 (247K miles/my daily driver)
'93 Volvo 940 Turbo Wagon (263K miles/a family truckster with spunk)
'99 Kawasaki Concours
Gravely 8120
Previous Vehicles:
'85 Jeep CJ-7 w/ Fisher plow (226K miles)'93 Volvo 940 Turbo Wagon
'53 Willys-Overland Pickup
'85 Honda 750F Interceptor
'93 Nissan Quest
'89 Toyota Camry Wagon
'89 Dodge Raider
'81 Honda CB 750F Super Sport
'88 Toyota Celica
'95 Toyota Tacoma
'74 Honda CB 550F

looky here, I'm posting in a crazy old thread!

My 95 e320 wagon is experiencing VERY similar symptoms.

I don't know if there is any correlation, but all of these things happened suddenly. The other day I was accelerating a bit briskly from a stop sign when I heard a "noise." not sure if it was a pop or bang but whatever it was it made the car stutter and had significant power loss and was loud enough for me to look backward to see if I lost a part or hit something. gave it throttle and suddenly it surged forward and behaved. Every since that moment the car has been sick. idles really rough but hasn't stalled. starts fine, and runs smooth at higher RPM. power loss is present at slow speed/acceleration (like in a parking lot). I did a quick scan of all vac lines any they look okay. where is the ERG valve on these puppies...is it the one above the exhaust manifold toward the firewall? cuz the connection looks fine, but is there a way to bench test it?

it looks like its been a while and hopefully you fixed your problem by now, but if you haven't... check your injector seals - spray some 2+2 around the injector seal at the head and look for bubbles or any change in idle. look hard - a small leak can be hard to detect and cause a lot of problems. new injector seals (o-ring, nylon seal and rubber boot to seal injector to nylon sleve) cost ~$6.00 per cylinder and easy to install. i had the exact same symptoms with my 89' 300 te and this fixed it and it was a very small leak!