2002 Isuzu Axiom gasoline smell

I'm trying to help my father-in-law. When you start the vehicle there is a raw gas smell. It goes away when you begin driving. It returns if you are stopped at a light for a few minutes and goes away when you begin driving again. This is my father-in-law's vehicle. I am a mechanic visiting from out of state. I specialize in brake/suspension/drivetrain and own a restoration shop. I do NOT specialize in computer controlled systems. I have thoroughly checked out the gas tank and fuel lines, vapor/vacuum connections, manifold, throttle body, etc. The vehicle has been taken to local mechanics and as well as the dealer with no success in finding the problem. I'm wondering if it is some kind of issue with the computer and communication with the TPS that may provide an over rich mixture at idle or something like that. I have had no luck in finding a TSB covering this issue and I have no access to any diagnostic equipment while I'm here. I'm certain there are no external leaks unless there is a high pressure leak that completely vaporizes into the air and leaves no evidence other than smell. Any suggestions?