Hi all, here is some info from General Motors
The installation of an aftermarket reusable, oiled air filter may result in:
Service Engine Soon (SES) Light On
Transmission shift concerns, slipping and damaged clutch(es) or band(s)
Engine driveability concerns, poor acceleration from a stop, limited engine RPM range
The oil that is used on these air filter elements may be transferred onto the Mass Air Flow (MAF) sensor causing contamination of the sensor. As a result, the Grams per Second (GPS) signal from the MAF may be low and any or all of the concerns listed above may occur.
When servicing a vehicle with any of these concerns, be sure to check for the presence of an aftermarket reusable, excessively oiled air filter. The MAF, GPS reading should be compared to a like vehicle with a OEM air box and filter under the same driving conditions to verify the concern.
Transmission or engine driveability concerns that are the result of the installation of an aftermarket reusable, excessively oiled air filter are not considered to be warrantable repair items.
Whats it mean? Take out your K&N filter before going to the dealer, or better yet just clean the Mass air flow sensor yourself, just use spray type brake and parts cleaner.