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1994 C280
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111 Posts
Discussion Starter #1
Hi Team

After hours and hours of reading, I still haven't been able to solve my problem.

I have a 1994 C280. When idling it stumbles "slightly" and there is a low frequency vibration. It is more noticeable in neutral (I assume) as the engine is unloaded. The car has a new Wiring Harness, New Plugs (Bosch F8DC4), New Engine Mounts, New Transmission Mount, new fuel air filters and has been run on Mobil 1 and 98 octane fuel since day one.

I think this car does not have an EGR system as it is not visible on top of the exhaust manifold, but it does have this bit

http://www.peachparts.com/shopforum/attachments/tech-help/1886d1019761724-stripped-retaining-screw-ignition-coil-1994-e320-no-egr2.jpg Is that related to the EGR?

No check engine light (the car doesnt have one)

It stumbles even with the MAF unplugged, and also when just started in the morning, however a bit more pronounced (I assume this rules out the O2 sensor as that wont be operating yet)

I also have not been able to correlate the idle issues to coolant temperature accurately. Seems to always be there

I know someone is going to be first guy in and say vacuum lines, but please be specific as I have done the best I can checking for leaks with some brake cleaner.

I think the purge valve is a place to look, but I have very little understand of what or how.

Thanks Guys,:bowdown:
 

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2002 ML55 AMG, 2005 Chrysler Crossfire Coupe Limited, 1999 C280
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4,714 Posts
I'm no expert but with engine and transmission mounts taken care of, I can only think of your drive shaft and/or bearings.

Others will chip in soon, hopefully.
 

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1994 C280
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111 Posts
Discussion Starter #4 (Edited)
Thanks FAR888 & jc1kz for your replies.

I think I can rule out the drive-shaft as when the car is moving (drive-shaft spinning), it runs like new. Only when stationary does this seem to be a problem, or maybe I can only notice it when the car isn't moving

jc1kz, My car is not a American one, it is a European one, and I cant see the EGR system on the exhaust manifold. Is it on the top or bottom of the manifold?

Also, what is the pipe running into the intake, to the right of the Power Steering reservoir in this picture? (not my car BTW)

http://www.peachparts.com/shopforum/attachments/tech-help/1886d1019761724-stripped-retaining-screw-ignition-coil-1994-e320-no-egr2.jpg

Thanks once again for your assistance
 

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1994 C280
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111 Posts
Discussion Starter #5
I should also mention that it revs up all the way to red line with no complaints at all, and fuel consumption is still on the dot with what it were when it was brand new.
 

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2000 C230 Kompressor
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141 Posts
That pipe in question isn't EGR related as it has rubber components to it, and would melt under the extreme heat. Does your car have an OBD connector at all? My old 95 Nissan has an OBD I connector and I've used its data readout to see throttle position, coolant temp, o2 sensor, and most importantly fuel trims which is a big help in diagnosing engine related problems
 

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1994 C280
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111 Posts
Discussion Starter #7
Hi flip240,

Yes it does have an OBD port, however I dont think you can pull the sort of data you get with a OBDII compliant vehicle from it. I was under the impression that the fuel trims ect are all electronically controlled and no manual intervention is possible.No codes either.
 

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1994 C280
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111 Posts
Discussion Starter #8
Some more info:

Sometimes in the mornings when I start the car it starts a little bid odd. Let me elaborate.

If the normal crank and then start sounds like "Ca-huhahuha" and then its running, the "Ca" being the starter motor engaging, "huhahuha" being the cranking.

Some mornings it just goes "ca-hu" and before the first "ha" the engine is running.

Apologies for the comical description, but I felt it was the best was to describe this.
 

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2010 E350, 2005 Tundra Sold the 1998 C230
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322 Posts
Some thoughts:

As part of the new electrical wiring, have the coil packs been replaced as well?

What kind of diagnostics does this car have, are there codes to read? Its before odb2 and European, so I'm just not sure.

Have you been able to put a vacuum meter on it running at idle and see what that looks like? Lots of vacuum hoses on these cars and not all visible at first glance. Check Your Engine’s Health: With a Vacuum Gauge | Tuner University

Has the MAF been replaced? May be shotgunning it but sometimes replacing troublesome parts early on has been known to work.

Any cleaning of the injectors been done? I know on some cars they can hook up to the fuel rail and run in a special cleaner to do the job, or you can always dump a can or two of seafoam or some other type of chemical in the tank and see if that works.

That's my initial take on it, let us know how it goes.
 

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1994 C280
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111 Posts
Discussion Starter #10
Some thoughts:

As part of the new electrical wiring, have the coil packs been replaced as well?

What kind of diagnostics does this car have, are there codes to read? Its before odb2 and European, so I'm just not sure.

Have you been able to put a vacuum meter on it running at idle and see what that looks like? Lots of vacuum hoses on these cars and not all visible at first glance. Check Your Engine’s Health: With a Vacuum Gauge | Tuner University

Has the MAF been replaced? May be shotgunning it but sometimes replacing troublesome parts early on has been known to work.

Any cleaning of the injectors been done? I know on some cars they can hook up to the fuel rail and run in a special cleaner to do the job, or you can always dump a can or two of seafoam or some other type of chemical in the tank and see if that works.

That's my initial take on it, let us know how it goes.
Hi Aquinob.

This car has OBDI diagnostics.

The coil packs were replaced and so were the leads. How would I hook up a vacuum guage to the car and what would I expect.

I cant see how the injectors would have become dirty, it has always had a new fuel filter every 4 years, and only run on 98 octane fuel. It has had some 3m injector cleaner through it, but no luck.

I would also like to check the resistance (in case one was a dud from new) of the wires, but cant find any data on what it should be

I have not replaced the MAF, and find it very hard to suspect it, as the symptoms persist with it unplugged, and even when cranking sometimes (before the MAF takes over). I had a look at the intake air temp sensor - clean as a whistle but can this be the problem? Any way to check it?

Can someone knowledgeable about the purge valve please chime in on how to check this?

Thanks again.
 

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1994 C280
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111 Posts
Discussion Starter #11
Hi again everybody,

My locks dont work, never bothered me as I never need to lock the car. Could this be related?
 
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