94 Grand Prix GTP Idle issues

I recently replaced my intake gaskets. There is absolutely no vacuum leak. The mass airflow sensor tested good. my fuel pressure is 2 lbs under normal. when the car is in park, it idles very low and revv's in between 500 and 1000 rpm then dies eventually. when it is in drive, it does this same thing. it takes awhile for it to start doing this, it usually take 5 minutes or so after it warms up it starts this strange prblm. can my low fuel pressure cause this? thanks. no errors stored in computer either. chevy dealership checked it for them and they ended up giving the car back to me telling me they were stumped.

2 pounds low on fuel pressure will not cause this unless when you rev it up the fuel pressure is not increasing. Put a guage on it to insure that the pressure rises when the rpm's go up. If not you may need a new fuel pressure regulator or a fuel pump. The other item is did they clean the Idle air control motor. It works both hot and cold and when the motor gets hot it may be sticking. You can clean it easily with throttle body cleaner. Don't know if it will help but you never know.

hey thanks for the help, it ended up being my o2 sensor was very very glitchy.