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Hello all. Due to the cold winter here in Michigan, I haven't been driving my 2007 CLK550 Cabriolet very much (less than 10 times since November). When I drove it a few weeks ago for the first time in about two weeks, a check engine light came on near the end of my 25 mile trip. Fortunately I had my scanner on me and the codes came up as: P0172 - Mixture in the right cylinder bank is too rich when idling. P0175 - Mixture in the left cylinder bank is too rich when idling.
This causes a rough idle once the car is warmed up a little. The main thing to note is how the RPM's fluctuate at idle. Other noteworthy symptoms are how the gear shifts are sometimes followed up by an awkward rev and that it has stalled on me twice while under these conditions (running rich).
I read all over the internet looking for what could cause this. The most common answer was the MAF sensor, so I replaced it with a brand new OEM Bosch MAF (I did this after cleaning the old one with MAF cleaner, to no avail). Changing the MAF did not solve the problem as the CEL and same codes came back shortly after. Moreover, my scanner showed identical Air Flow Rate (about 9-15 g/s at idle) values with both the old and new MAF.
I've changed the air filters with OEM Mann filters and made sure the Air Filter Housing was installed snug and all hoses were fitted correctly. I've also cleaned the throttle body with throttle body cleaner and took it for a couple drives under various loads (normal driving and fun driving).
My next guess is either a vacuum leak or Oxygen Sensors.
Does anyone have some insight on this issue? Any feedback would be tremendously appreciated.
Last edited by Nahhas26; Jan 14, 2017 at 04:28 PM.
Thank you for the response Rudeney. My scanner (Creader VII+) actually was able to pull up the more specific codes you referred to.
Now would you suggest that I replace the pressure sensor indicated in the picture in your last post, or is there some steps I should take prior? Also, is there any values in specific that I should check in the Freeze Frame/Data Stream that would help?
I'm not sure if this is relevant to the issue or not, but the car did fail one EVAP test (0.040") as shown:
I think it failed because I never took the car out for a proper drive cycle while I was reading these codes and values. However thats just my educated guess.
So I sprayed starter fluid (I had a fire extinguisher on hand) around hoses and places that I felt could have a vacuum leak and felt no rev or anything. Then I sprayed around more random places looking for a rev and nothing. My next guess is the MAP sensor and upon removing it I broke a tab that holds it in place . To take off the hose that attaches to it, do you just pull on it while twisting? Or is there a proper way to remove it? Same goes for the cable plug? Picked up new MAP sensor today and plan on replacing it today hoping for healthier idling.
So I replaced the MAP sensor and, initially, it was seemed symptom free so I cleared the codes. But after the second drive the CEL came back on. Same codes, but now 3 I/M Readiness tests failed. Before changing the MAP, all 8 I/M Readiness passed. The car is still coughing at red lights and idle (once warmed up), and even has a rough first shift.
I feel like I have checked everything. I'm thinking fuel pressure regulator now? But I don't have much of an idea of how to check that. I'm sure I can figure it out with some research.
This stupid CEL is driving me insane now.
Anybody have any helpful info they could share? Would be greatly appreciated.
Yes, the stored codes are the same. As far as the readiness tests, I did not drive far enough to complete a proper cycle which may be why they did not all pass.
Just checked the purge valve by taking it out and checking if I can blow through it, as it should be closed when there is no power to it-- I was not able to. So I guess the purge valve is not defective.
After doing some reading around, I have learned that the fuel pressure regulator is in the fuel filter.
Is there any values I can check on my (somewhat) professional scanner to check the fuel system and identify a problem in the fuel pump or fuel pressure regulator/fuel filter?
Will your tool give you actual values for the self adaptation? If so check the adaptation values at idle. It will be towards the negative or positive limit of 5%. Please see if it's negative or positive. You will not be able to read fuel pressure other than the manual way.
Ok so definitely trying to lean it out. Have you checked the large hose that goes from the oil centrifuge cover to the air mass/tb elbow? If that's good definitely move on to fuel pressure test.
Just finished testing the fuel pressure under various conditions. In "run" mode, with the engine off, the fuel pressure is 30 psi. With the engine on it was a constant 55 psi with nearly no difference when put under 2-3000 rpm. When the engine was turned off the psi dropped to 50 and stayed there for 10 minutes, then I took out the fuel pressure gauge.
I did check the hose that you mentioned Rocman8, it appeared to be fitted snug.
My next guess is o2 sensors or an undetected vacuum leak as my starter fluid method may have overlooked a small leak somewhere.
At this point I may just take it to a mechanic to have them just diagnose it, but we all know how that goes .
The only times I've seen the adaptation go that direction was because of the air mass sensor. Did you reset the adaptations or let it idle long enough with the new one before putting the old one back in? Are you sure you got a good one?
When I got the new Mass Air Flow Sensor, I performed a multimeter resistance (ohms) test on the new and old MAF and the values were nearly identical. This led me to believe that the old MAF was not faulty, but I replaced it anyway and drove with it for about two weeks and the symptoms did not go away.
If you could, please explain how to reset the adaptations.
I believe I did let it idle when I put the new MAF in, I do not remember how long exactly. But the drives with the new MAF in often reached 25 miles/ 50 miles round trip (to school and back).
I would not rule out the possibility of having received a faulty MAF. Perhaps, I will try getting a replacement.
Does anyone know where to get the proper specifications (fuel trim.. etc.) for my model?
Ok if you drove it that long with a new air mass, correctly seated intake housing and factory filters then that would be more than enough for it to adapt on its own. So if you didn't get a faulty air mass off the shelf then I'm lost as to what it could be now. I suppose a front O2 sensor can cause this.
Hello again and thanks for the feedback. I've had the CLK stored for a while now, its in my home garage again and that damned CEL is still on but now after a couple weeks at home its also smoking noticeably from the passenger side of the engine compartment. It looks like its coming from the exhaust manifold. I know an oil leak is a common diagnosis for this however the valve seals in the back of the engine that I know go bad often do not seem to leave any oil residue on my hand or a napkin when I feel around there. Smoke is a either a new problem or my running rich problem just evolved.
To recap: CEL - P0172 P0175 (engine running rich at idle in bank 1 and bank 2 cylinders; enleanment compensation reached a limit (25%). Short term fuel trim at idle fluctuates in both banks from -25% to +25% at times. Long term fuel trim is about 8-9% in both banks. Engine shakes and even stalls sometimes (all symptoms only at idle).
Tried changing MAF twice, MAP, cleaned throttle body, checked fuel pressure, checked purge valve, changed air filters, tried running a full tank with fuel injector cleaner. Always run premium gas.
Mechanic said both Oxygen sensors, which is rare. He didn't do any extensive testing, which makes me iffy. I've tried everything so why not this?
As far as which O2 sensors to change, do I change the upstream or downstream sensors? Is there 2 sensors per bank (B1S1, B1S2, B2S1, B2S2) My knowledge lacks in this area, I just learn as I go
Any suggestions/comments/questions are welcome.
Last edited by Nahhas26; Mar 23, 2017 at 03:32 PM.
So it was oil leaking. The source was the left-most (passenger side; back of the engine) engine oil separator cover that has the hose connecting to the MAF. It has 4 star screws in it. Using a handy mirror, I saw a very very slow leak and everything around there was discolored. The same place on the other side of the engine was beautifully clean.
I'm not sure what to do with this information now. Did the oil leak poison the oxygen sensors? Is this a common problem? I know that those covers in the back of the engine go bad often, however I thought it was usually the smaller ones without the screws in them.
With this new information, can someone shed some light on me?
Last edited by Nahhas26; Mar 23, 2017 at 05:48 PM.
Each of those two OBDII codes relate to three different MBZ-specific DTCs with different diagnostic steps and potential causes, including a bad MAF sensor, pressure sensor, O2 sensors, vacuum leaks, and even a weak fuel pump. You're going to need to get a proper diagnosis if the codes persist.
As for the leak, replace the cover on the oil centrifuge - it's cheap and takes only a few minutes. You also need to clean up all the oil, including in the connectors for the O2 sensors, located below the bell housing. That may solve the errors if those connectors were soaked.
Thanks Rudeney, I ordered the Oil Centrifuge cover, it should be here in a couple days. Do you know what values should come up when putting the Oxygen sensors on a multimeter test?
So I'll remove the Oil Centrifuge cover, clean up the oil residue, take out the O2 sensors, clean them, multimeter test them, put them back in (if they're good?), put on the new Centrifuge cover, and hope for the best.
I don't know of any way to do a simple resistance check. SDS uses a special breakout box that plugs in between the ECU and it's wiring harness and allows for probing of various circuits. It mentions testing current consumption of the heating circuit (1.0 -3.5 amps), but that's it.
After spilling some oil on the manifold, my car smoked and smelled for a couple of days. It then threw a CEL light and ran rough. Got some good advice from our forum ,I have a dealer about 20 miles, and a independent MB mechcanic about the same distance. I took it to the indi. He pulled the same codes as your are showing, and traced it back to a faulty purge valve. Total cost..$250. the new valve was $85 the rest was labor. Not being a mechcanic I thought it was a fair deal.
Picked the car up the next day, they cleaned and vacuumed it as well.
It has ran smooth as glass since, and no CEL.
If I have problems in the future, I will use them again.
thanks to everyone on the forum for help, and guidance.
regards
dk
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. To take off the hose that attaches to it, do you just pull on it while twisting? Or is there a proper way to remove it? Same goes for the cable plug? Picked up new MAP sensor today and plan on replacing it today hoping for healthier idling.
