All right, I know this sounds crazy, but my 98EXV6 performs better without the gas cap on than with. I had noticed about a month ago that my gas mileage was taking a tumble and the engine was having to work much harder it seemed than usual- ie rougher shifts, more shifting when going up hills, higher RPM's etc.

Well on my way down to Florida I forgot to put the gas cap back on and went on my way. 50 miles later the check engine light came on so I pulled over and checked the fuel door and realized what I had done. Well I kept driving and noticed that the RPM's weren't as high, and I was getting GREAT mileage as well as the car performing like it used to. I eventually replaced the cap and now the car is running like crap again and gas mileage sucks. Anyone have a clue what is going on. Any suggestions would be great.

Thanks