COuld be too much oil, goto PepBoys and buy CRC Mass Airflow Sensor cleaner and clean any oil or dirt off your MAF, reinstal the stock filter and see if the problem comes back. If you really want the KN installed, wash the oil out of it and install it w/o oil but if you do this it will filter less.
Are you sure it was installed correctly? Make sure you did not put the new filter back in backwards. It has to be facing a certain way. I would also check your hose to the M.A.S. and make sure it did not come loose.
Hybrid Mode
