That is one of those codes that is stupid in my mind and nearly impossible to chase. I hope your state doesnt have emissions testing. I have heard of people selling their vehicles because they gave up on chasing that code. As much as I hate saying it, I would take it to the stealership and have them do the diagonsis. Edit. Did you check to make sure when you changed your gas cap that there is no corrosion or rust built up on the sealing surface at the filler?