Deviation rich (both banks), rough idle

I am getting codes for lambda adaptation deviation rich in both banks. I also have an idle drop problem (engine idle RPM will drop and feel like its about to stall before recovering).

I tried unplugging the MAF and the idle drop issue seems improved but not completely solved.

I tried spraying carb cleaner near vacuum leak prone places but found nothing (near intake boot, CCV). Also, wouldn't deviation rich indicate that it is NOT a vacuum leak? (That would cause deviation lean, right?)

I am ruling out O2 sensors since it is both banks. Good assumption?

This leaves in my mind just the MAF sensor itself. I would rather not spend the money to replace the MAF sensor unless I am pretty confident that that is the problem. This is on my 01 330Ci. I also have a 99 323i, anyone know if these MAF sensors are interchangable? Appear to be different part numbers on realOEM so guessing thats a NO.

Anyone have any input for further ways I can diagnose without beginning to throw money at the problem?

Thanks,

Dan

Not likely the MAF sensor, O2 sensors or any other sensors.

Deviation rich means you are running LEAN.

You likely have a vacuum leak.

Check the lower CCV oil return hose, fuel pressure regulator vacuum line at the filter and see the first 2 links below in my signature.

Originally Posted by jfoj

Not likely the MAF sensor, O2 sensors or any other sensors.

Deviation rich means you are running LEAN.

You likely have a vacuum leak.

Check the lower CCV oil return hose, fuel pressure regulator vacuum line at the filter and see the first 2 links below in my signature.

Ahh, ok, had it backwards. Makes sense I guess (ECU trying to richen fuel/air mix and deviated too far in that direction). Thanks. I will continue searching for a vacuum leak. Do you or anyone have suggestions on any other creative ways of tracking it down besides just checking the common places?

Hi OP, keep us posted.

Smoke test, spray brake cleaner, mechanics stethoscope with the transducer removed and extending the hose to listen for vacuum leaks.

But except for crack valve cover or bad valve cover and a few other odd things a visual inspection is really the best solution. You WILL find problems visually inspecting the obvious culprits and you will likely find other problems as well.

Originally Posted by jfoj

Smoke test, spray brake cleaner, mechanics stethoscope with the transducer removed and extending the hose to listen for vacuum leaks.

But except for crack valve cover or bad valve cover and a few other odd things a visual inspection is really the best solution. You WILL find problems visually inspecting the obvious culprits and you will likely find other problems as well.

Valve cover gasket is indeed bad and leaking, but I would be very surprised if this could let enough air in to set off adaptation errors and cause a noticeable idle drop. My valve cover gasket was leaking way worse and the SAP vacuum line was cracked really bad on my other e46 and no CEL and perfect idle...

You would be surprised!!!

Also you can have oil leaking and not a bad air leak and you can have a bad air leak with no oil leaking!

Cracked valve covers are also another very common issue as well.

Do not discount the valve cover. A valve cover leak will likely not respond to a brake cleaner test very well, however, if you smoke test the crankcase you will find the valve cover leak quickly.

Hmm, ok. Well thanks for the advice, I'll definitely tackle the valve cover gasket before trying anything else then.