I was on a fairly long (180 miles) trip today...and as I hit the last leg of my journey, i stopped at BP and filled up the tank. When I started my car again, the "check engine" light came on for no apparant reason...no rough idle...no overheating, nothing. My best guesses are a dirty K&N filter (it really needs to be cleaned, either way), or perhaps an oil change (i just bought the car so I don't know when the last time that was done)and advice would be much appreciated!