My "check engine" light has been on for a couple of days now. In the manual, it says to make sure the gas cover was on tight. It wasn't - - it was on crooked so I replaced it and made it click. The manual says it should take 3-4 trips for the "check engine" light to go out. When I filled up yesterday, I noticed that the metal flappy thing that covers the actual entry into the gas tank (the hole where you insert the gas nozzle) is missing. Would that be the reason for the "check engine" light? Maybe it affects the pressure in the tank causing the sensor to light? Anyone had this problem before? Hopefully it is a cheap fix! Thanks.

Most likely that is not the problem. Having a good gas cap that seals properly is what the ECM looks for.