I changed my intake filter three weeks ago from K&N to OEM, and a week after the change decided to go back to K&N. After that my mileage has gone down from ~18mpg to ~15-16, which I thought was a drastic change considering my driving style has not changed, and I have pretty much the same route. Plus I'm not even using my A/C as much anymore since it's getting colder. So what's the deal here?

 

Did you put the filter in the right way and not upside down?
Just checking.

 

The K&N filter only fits in one way, so yea it's not placed in reversed.

Anyway, the problem seems to have been fixed. Maybe computer has adjusted. I did another calculation on my last fill up (miles / amount of gallons filled) and it came out to 17.3, which I'm fairly happy with since I've been running at high RPMs. I did notice that the Empty Tank light has been coming on early. No problems though.