1992 pontiac grand prix. cold start it runs 3000 RPM;s when it warms up it bounces between 2500 and 900 RPM's
You check it for codes? Try unplugging each sensor to see if it smooths out starting with the map sensor, unplug and plug it back in. Sounds like a bad map sensor though, could be a vacuumleak that wouldn't exactly explain the the ability to idle back down.
check the fuel pressure regulator. My 92 did the same thing. you will have fuel coming out of the vacuum line on the back side of the throttle body.
Search Pontiac Grand Prix Questions
Are you a UK consumer? CarGurus now has a discussion forum in the UK.
Pontiac Grand Prix Experts