Originally Posted by Z K
K&N has a vested interest in selling oiled filters... I know from personal experience that it definitely does have an effect on MAF sensors.
I've had K&N oil destroy 2 MAF sensors on a previous car. They ran fine prior to changing the filter. After install of the K&N and driving on it a while, the car started running very bad. Hesitation on throttle and low boost. Diagnosed as a bad MAF sensor. After taking the sensor out, you can see the intake tract and sensor covered in oily residue from the K&N. Put in a new MAF and it was fine for a couple of months then it happened again. Installed another MAF, ditched the K&N and never had a problem after that. I'll never run an oiled filter on a MAF equipped car again.
This may also have to do with the proximity of the MAF sensor to the filter. I ran a K&N on my 2004 350Z for 14000 miles with no issue whatsoever, however the Z has a long intake tube and the MAF was around a bend in the tube so it may have been shielded from oil deposits. In any case, shouldn't be an issue in the M3.