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Mercedes w202 C180 1996 | M111.920
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Discussion Starter #1
Hi all,

I have a small problem with my C180 1996 (german model). I live in Norway and it´s pretty cold this time of year (-15/-20 C). When I start the car it runs fine and there are no problems for the first 20 min (when its still cold), but when the coolant reaches 80 C (operating temp) the idle goes down. As long as I´m driving it´s fine, but when I stop the car(transmission in D) the idle drops, below 500 and then it stalls. If I quickly move set the car in N i´m able to make it but just barely.

I have a early model with MPS or Manifold Pressure System, so No it´s not the MAF. But I noticed that there is a pressure sensor at the air inlet, above the engine block. Could it be this sensor that´s bad? Any other ideas? Please anything.

Yeah, and this is not a problem in "warm" weather (0 C and up), so I was just thinking that maybe one sensor or something doesn´t work as it should when it´s really cold.

Thanks!
 

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2000 c230 Kompressor (Totalled 5/2012)
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238 Posts
I would absolutely look into the fuel pressure. Attach a fuel pressure gauge to the port on the fuel rail and obtain the readings under the following conditions: 1) while the engine is running, 2) after the engine has been off, 3) 5 and 10 minutes after the engine has been off. I don't think it's a fuel pump problem, unless it is somehow overheating. Sometimes fuel pump relays do fail when they warm up, so I would try switching yours with one known to work... it's an inexpensive part anyways. So try those two things for now.

I noticed something else in your post. I recommend also checking the fuel pressure regulator. It's a round part which is attached to the fuel rail. It has a black rubber hose coming out of it. Carefully pull off that hose and see if there is any fuel in it. If there is, that's almost a sure sign that the regulator has failed.
 

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1998 W140 S420 Green, 2000 W208 CLK230K Blue
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11 Posts
hello. i had similar problem on c200. check all vaccuum lines to lights, gearbox etc. i had broken headlight adjuster pipe and leaking pipe to auto box. also remove the vaccuum pipe to the ECU and clean it through. mine was full of very thick sludge and did not allow the manifold pressure to be measured quickly enough. the sensor in the air pipe from the filter is a temp sensor. the pressure is sensed in the ecu mounted on th inner wing. the pipe exits low down on the inlet manifold.
 

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2002 ML55 AMG, 2005 Chrysler Crossfire Coupe Limited, 1999 C280
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4,714 Posts
I don't know whether your particular model has a crankshaft position sensor.

If it does you may want to look into that.

Since it's temperature related you may also want to check any relevant temperature sensors.

ALSO, have you retrieved the diagnostic codes?

They will give us a good indicator of what is happening.
 

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Mercedes w202 C180 1996 | M111.920
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58 Posts
Discussion Starter #5
Thanks for all feedback.

Yes my car has a CPS, but wouldn't that fail in normal weather as well. I have read that these often fail (shorten) when the engine gets hot, but that shouldn't depend on the outside temp.

I don't have the gear to scan my car, but I'll try to do it somewhere.

Thanks guys.
 

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2002 ML55 AMG, 2005 Chrysler Crossfire Coupe Limited, 1999 C280
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4,714 Posts
Thanks for all feedback.

Yes my car has a CPS, but wouldn't that fail in normal weather as well. I have read that these often fail (shorten) when the engine gets hot, but that shouldn't depend on the outside temp.

I don't have the gear to scan my car, but I'll try to do it somewhere.

Thanks guys.
I am pretty sure I did not misread your original post.:)

In that post you did not refer to the ambient temperature you referred to the car's engine temperature.

I have a small problem with my C180 1996 (german model). I live in Norway and it´s pretty cold this time of year (-15/-20 C). When I start the car it runs fine and there are no problems for the first 20 min (when its still cold), but when the coolant reaches 80 C (operating temp) the idle goes down. As long as I´m driving it´s fine, but when I stop the car(transmission in D) the idle drops, below 500 and then it stalls. If I quickly move set the car in N i´m able to make it but just barely.
When your car engine temperature reaches 80 degrees centigrade that is normal operating temperature and, I submit, HOT.

One symptom of a failing CPS is engine cut-out or instability when hot.

Another symptom is failure to start when HOT.

Check if there are any diagnostic codes and post on here - Do the diagnostic test especially when the car is HOT (normal operating temperature) and manifesting the symptoms of which you complain.
 

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Mercedes w202 C180 1996 | M111.920
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Discussion Starter #7
I am pretty sure I did not misread your original post.:)

In that post you did not refer to the ambient temperature you referred to the car's engine temperature.



When your car engine temperature reaches 80 degrees centigrade that is normal operating temperature and, I submit, HOT.

One symptom of a failing CPS is engine cut-out or instability when hot.

Another symptom is failure to start when HOT.

Check if there are any diagnostic codes and post on here - Do the diagnostic test especially when the car is HOT (normal operating temperature) and manifesting the symptoms of which you complain.
Yes, thats correct, but if you read the last part in my post you can see that this isn't a problem with ambient temps above 0 deg C (summer/autumn). I.e. the problem should be present all year and any ambient temp since the CPS fails when the engine is 80 deg.
 

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2002 ML55 AMG, 2005 Chrysler Crossfire Coupe Limited, 1999 C280
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Forgive me, I am not seeking an argument here, but if the car has reached it's normal operating temperature of 80 degrees centigrade it shouldn't matter what the ambient temperature is since the car engine is HOT.

Put simply:

A car which has reached operating temperature in summer should not behave differently from a car which has reached operating temperarure in winter since the only temperature which matters is the operating temperature of the engine.
 

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1995 C280 (165K mi)
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A car which has reached operating temperature in summer should not behave differently from a car which has reached operating temperarure in winter since the only temperature which matters is the operating temperature of the engine.
Well said. I concur.

In regard to the CPS failing due to temperature, it has been noted in this forum that the failure is due to the engine temp NOT the ambient temp.
 

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Mercedes w202 C180 1996 | M111.920
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Discussion Starter #10
Maybe I misunderstood your post. I think maybe we are saying the same thing and I agree that it shouldn't matter what the ambient temp is in the case of failing CPS. That's why I don't think it's the CPS that is defective, because I didn't have this problem this summer/autumn, but I had the problem last winter as well. I.e. the problem is only present during extreme ambient temps(cold). I very much appreciate all the help and I will try to measure the resistance of the CPS this weekend (at 80 deg) to see if it's defective. I'll also check for vacuum leak and check the fuel pressure reg.
 

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2000 c230 Kompressor (Totalled 5/2012)
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Maybe I misunderstood your post. I think maybe we are saying the same thing and I agree that it shouldn't matter what the ambient temp is in the case of failing CPS. That's why I don't think it's the CPS that is defective, because I didn't have this problem this summer/autumn, but I had the problem last winter as well. I.e. the problem is only present during extreme ambient temps(cold). I very much appreciate all the help and I will try to measure the resistance of the CPS this weekend (at 80 deg) to see if it's defective. I'll also check for vacuum leak and check the fuel pressure reg.
Let us know what you find. But that's very strange that the problem went away for the spring and summer and then returned. I would have your battery tested too and if it's fine, make sure it's receiving the appropriate current from the alternator. The reason I am mentioning this is because, under extreme cold, batteries can have trouble... especially older batteries. You would be surprised how many things can malfunction with even a little variance in battery output.

Is there any way you can check for malfunction codes? Maybe you can take the car to a shop and they'll do it.
 

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Mercedes w202 C180 1996 | M111.920
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Discussion Starter #12
I'll post my findings...when I get there.

My battery is pretty new (2y) and the alternator as well (1.5y). I did take out the battery the other day to fully charge it, as you say in cold weather a 70% battery may not do it for the car, so I don't think it's the battery or alternator. But to be completely sure I'll measure the charging current.

I'll do my best to scan the car. But as you may know this car doesn't have the OBDII interface, but some old MB 38pin so can't buy one of these cheap readers.

Thanks for the feedback!
 
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