A couple months ago I installed a K&N FIPK. At the same time I cleaned the throttle body and MAF sensor. Prior to installing, my dash mpg calc. said I was getting 10.5 city/13hwy +/-. After the install I took a short 1.5 hr. round trip and the calc. said I was getting 16.5-17 @70 mph. Around town the mpg's did not change. Last Sat. I re-cleaned the MAF and was getting 13-14.5 around town all day into Sun. !! Now, 5 days later I'm at 12.5-13(town). Is this caused by the oil on the filter messing up the sensor? How often should it be cleaned and can it be cleaned to many times?