before i did my custom CAI i did a k&n replacement and really didn't feel any improvements but i knew it was breathing better then the stock paper filter. the only thing i have read in the forums when using a oil filter is to make sure you clean the MAS twice a year like OMEY said. CRC makes a MAS cleaner and i m about to clean mine here pretty quick . i assume you spray the MAS but not sure if i m suppose to spray the sensor . just waiting on OMEY to reply to the topic so i know how. i m also using a K&N filter on my CAI