ncmudbug

I'm having a slight problem. My wife's '06 C230 was due for a tranny fluid change so I took it to a shop a buddy of mine used. He had what seemed to be a particularly complicated problem and it seemed like they were very thorough, finally getting my buddy's car going again. Now I'm wondering if they took so long on my buddy's car because they don't know what they're doing.

After they changed the fluid, the car drove home fine. The next morning, after startup from cold, it would have an oscillating idle - faster than normal and then slower. I had my wife shut it down and I checked to see if there were any codes - none. She drove it without incident the rest of the day. Today she said it did the same thing so she revved it a little and she said it started behaving again. This evening, we were coming home and the CEL came on. I read the codes (P0170 and P0173 each of them displayed twice(?). The scanner software says that one set of P0170 and P0173 are stored and the other set are pending. There didn't seem to be any driveability issues before the CEL came on (I noticed it just as we drove into the garage.

It seems that it could be a vacuum leak. I took off the air filter housing but didn't see anything obviously disconnected or damaged. From my reading of the procedure to change the tranny fluid, there didn't seem to be any vacuum hoses that would be disconnected.

Does anybody have any ideas?

Thanks!

ncmudbug

Ok. I thought there might be a vacuum leak because I looked up the wrong code! It seems that I need to clean the MAF. Does that seem right?

I'll try that tomorrow.

cm60k

I think you have problem with fuel/air mixture, did you try to delete those codes..?

ZAYED,,

ncmudbug

Yeah. I haven't tried it yet. I Read further and found that it could be a vacuum leak after all if the MAF is good and clean.

cm60k

Try to delete them, then switch the car off-on, then see if they will comes back or not...

ZAYED,,

ncmudbug

Update: I just took it for a short drive through the neighborhood and it seemed to drive fine. The only thing I notice was the idle was slower than I expected (~600 rpm) but it was smooth. So far, the codes have not returned.

Z, do you suspect that it will "fix itself"?

cm60k

You may have loose in some place, MAF/air hose couplers, have to check those, during to gear oil changed, something been loose...!

ZAYED,,

ncmudbug

Thanks, Z! I'll pay particular attention to that when I take the MAF off to clean it.

It is pretty straight forward to take it off and put it on, right?

cm60k

Yes mate, you can tell..

ZAYED,,

Glyn M Ruck

Is the airbox clipped down firmly over the MAF? Indy's usually remove them for access & then don't clip them down tightly at the rear on the M272. This causes the MAF to hunt. Then you throw fuel trim codes.

ncmudbug

That doesn't appear to be the issue, Glyn. I popped it off looking for vacuum hoses that may have come loose and put it back on. I have been guilty of not clipping it down tightly in the past so I'm a bit more aggressive in checking that it's fully seated.

I'm going to have my go at cleaning the MAF today but this morning it had the same idle issue (oscillating between 800 and 1000) till it warmed up a little and then it was fine. So far no codes but if the condition isn't any better, I would expect them later if I don't do anything.

ncmudbug

Just thought I'd post an update.

I cleaned the MAF and the throttle body (for those contemplating this, there is different cleaner for each. You should be able to get it any reasonably supply auto parts store). The throttle body was difficult to get good access to because on the V6 engine, it is in the back near the firewall. An inspection mirror is really handy here. It seems the MAF includes the tube it's in. That confused me because all the pictures I'd seen looked like it would come out.

I put it all back together and it drove really well but the final test was when Mrs. NCMudbug took it out this afternoon because it was dead cold. The only problem was a squeaking brake! No CELs, not hunting on cold idle - or any idle for that matter.

Thanks Glyn and Zayed for your help!