Pontiac Problems? Ask a Mechanic for Answers ASAP
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This could be an actual evap leak which can be due to a faulty fuel filler neck or a hole in one of the evap lines.
a faulty a vent solenoid or a fuel pressure sensor those are the possibilities.
the evap system should be smoke tested to eliminate a leak concern or find one.
the naked eye will not spot a leak without the smoke, the filler neck can look rusted but may not be leaking, and to replace parts on a guessing basis can get expensive, not much you can do other than replacing a gas cap.