I have a 95 corola that I occasionally need to drive. It sits alot and the fuel tank rusted and I had it replaced. The car now builds pressure in the tank to the point that it starts to flood out the engine at low rpm, it starts to do it after about 20 minutes of driving. I unloosened the gas cap and the air comes whistling out If I leave the cap loose it runs fine I cant quite figure it out so if there are any ideas I would appreciate it...

 

One of the lines going to the tank is a vent. And it sounds like your tank isn't venting. There might be a bend in the vent line, rust in the line, a crimped rubber hose connection, or your charcoal canister could be plugged.

 

It would vent through the charcoal canister I would guess, the tank vent lines and everything is new. I will check the charcoal canister. Thanks