Gas fumes from under the hood

[DonJ]

I have a 90, toyota 4x4 pickup, 3.0, manual trans. I have had two tune-ups done and had the fuel filter replaced each time. After the first tune-up, I began to have intermittent gas fumes from under the hood on the passenger side. The fumes do get into the cab. More noticeable on the passenger side. This went away on its own. But, this happened after the second tune-up, too. Now it has not gone away. However, it will go months without doing it. Most of the time, if you shut off the engine, let it sit for a second, then restart, there are no gas fumes. I have had the fuel lines, charcoal canister, etc. check at two different shops. They do not know why this is happening. It does not matter how full the tank is or what the temperature is outside. Has anyone had this problem? Or does anyone have any ideas on what to look for?
Sorry for the long post, tried to cover everything.
Thanks for the help and info.

 

[WristPin]

make sure the vent tube in the tank/ filler neck is not pinched/ plugged.

have you pressure checked the cap?

perhaps the fuel filter is installed backwards.

 

[Jukelemon]

Perhaps you are running rich and since your fresh air vent into the cabin is on the right side, your passenger is smelling it. It is odd that a code is not thrown BUT that does not mean you are still not running rich.