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Persistent Cold Start Idle Drop Error After Timing Chain & Oil Pump Issues – 2011 C18
Hi everyone,
I’m dealing with a persistent issue on my 2011 Mercedes C180 1.8 CGI Avantgarde (M271 engine) with 350,000 km.
About 2 years ago, the engine started making timing chain noise. We replaced the chain, but the noise came back. It was replaced again under warranty, but the issue persisted. After that, we imported original parts from Germany, including the timing chain and camshaft adjusters (VANOS units), and installed them.
Later on, the engine was disassembled again and we discovered that one of the oil pumps had seized. Since a brand-new original part wasn’t available at the time, we installed a used oil pump. About a year later, the oil pump chain guide broke, and the engine had to be opened again. This time, the oil pump was replaced.
However, throughout this entire process, one issue has never been resolved:
On cold start, the engine idles at around 1500 RPM, then drops to normal idle
As the RPM drops, the check engine light comes on
If the idle is set slightly higher than normal, the error does not occur
In warm weather, the issue is rare or doesn’t happen
In cold weather, it happens consistently
Sometimes the error stays, sometimes it disappears on the next cold start
Additional info:
Throttle body is new (Bosch)
Adaptation/calibration has been done with original Mercedes diagnostic tools
I have also attached a photo of the error code for reference.
At this point, I’m not sure if the issue is related to oil pressure, timing system tolerances, or sensors.
Has anyone experienced a similar issue or can suggest what to check next?
Thanks in advance.
Error Codes: P006800,P001177,P233722
Last edited by seainn99; Apr 21, 2026 at 06:31 AM.
The trouble codes point to 3 distinctly different failures, which you have probably seen on your scanner descriptions.
-Mismatch in information received from air flow and throttle position sensors
-Camshaft timing errors
-Combustion knock sensor cylinder 2
Since increasing idle speed remedies errors and the throttle body is new, possibly the MAP (MAF?) sensor is at fault.
The trouble codes point to 3 distinctly different failures, which you have probably seen on your scanner descriptions.
-Mismatch in information received from air flow and throttle position sensors
-Camshaft timing errors
-Combustion knock sensor cylinder 2
Since increasing idle speed remedies errors and the throttle body is new, possibly the MAP (MAF?) sensor is at fault.
Thanks for your input.
I understand the different fault categories, but since the issue mainly occurs on cold start and disappears with higher idle, it seems more related to cam timing behavior than a sensor issue.
If it were MAP/MAF, I would expect the problem to be consistent rather than dependent on temperature and RPM.
So I’m leaning more towards a timing control issue (possibly solenoid/magnet related).
I do think the knock sensor issue is incidental to whichever one of the other is at fault. Your point on the adjuster solenoids when cold could be the point. I also thought about the locator pin on the adjusters being bent and not latching properly from that, but checking that would take going into them again, possibly for no gain.
Since it is only on a cold start at low temperatures, it could also be something in the open cycle system where many of the sensors are ignored. Those problems are very hard to find.
I do think the knock sensor issue is incidental to whichever one of the other is at fault. Your point on the adjuster solenoids when cold could be the point. I also thought about the locator pin on the adjusters being bent and not latching properly from that, but checking that would take going into them again, possibly for no gain.
Since it is only on a cold start at low temperatures, it could also be something in the open cycle system where many of the sensors are ignored. Those problems are very hard to find.
That makes sense.
I did some research and found that in cold conditions, if the camshaft magnets don’t actuate properly due to low oil pressure, it can cause this kind of issue. It also seems to match the behavior, since increasing idle RPM makes the problem disappear.
Is there a way to check the camshaft magnets without removing too much? For example, if there is oil inside the connectors or around the magnets, could that indicate a problem?
Oil inside the connectors is definitely a problem. It has to be addressed because oil can migrate along the wiring harness. The oil itself can damage every plastic connector it touches and can even get into other sensors and the ECU. The additives and contaminants it carries are even worse. If you have oil in the magnet connectors they need to be replaced and the cam position sensors, the crank position sensor, and the ECU connector need to be checked.
Oil inside the connectors is definitely a problem. It has to be addressed because oil can migrate along the wiring harness. The oil itself can damage every plastic connector it touches and can even get into other sensors and the ECU. The additives and contaminants it carries are even worse. If you have oil in the magnet connectors they need to be replaced and the cam position sensors, the crank position sensor, and the ECU connector need to be checked.
Thanks, that’s very helpful.
I’ll first check the connectors myself to see if there is any oil present. Then I’ll have the camshaft magnets inspected and get back to you with the results.
The car gave the error again today, so I’ll also scan it again to see if there are any additional fault codes.
Oil inside the connectors is definitely a problem. It has to be addressed because oil can migrate along the wiring harness. The oil itself can damage every plastic connector it touches and can even get into other sensors and the ECU. The additives and contaminants it carries are even worse. If you have oil in the magnet connectors they need to be replaced and the cam position sensors, the crank position sensor, and the ECU connector need to be checked.
Quick update:
I scanned the car again after the error came back. This time I got:
P254009
P006800
The issue still behaves the same:
Happens on cold start when RPM drops
Does not occur if I increase idle or give slight throttle
Much less noticeable in warm conditions
I will check the camshaft magnet connectors for oil and report back with what I find.
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