this may sound kind of stupid but after having someone loosen my lugs last year and almost lose a tire at 70+ and having death threats against me, my car started idling like someone sugarred the fuel tank, well to make a long story short my fuel door kept popping open not because somoene pried it open (pcv valve caused bad idle) but because dirt and dust etc got onto the little black plastic piece that holds the door closed, and with this dust,dirt etc it would slip open going over bumps or just driving along, after i waxed my car a few weeks ago it started happening again, all you have to do is make sure the black piece and the clip that holds the black piece to the car when the door is closed are clean.... hope this helps