What is wrong with my car? Now and then won't keep RPM. If left alone for hour it fixes itself?

(2011-03-20 14:20:24) 1. Joe Dirt Says: Took it to shop and they couldn't find problem but they let it sit around for 3-4 hours before they hooked it to a computer and it stopped acting up and ran ok by then. what could be wrong with my car?2. mdk68gto, ase certified m tech Says: it could be an idle air control valve, a bad mass air flow sensor, so many things.3. vince k Says: you need to give more info. what kind of car and motor? After it sits it runs fine for how long. does it die at stops, while driving, idling in park?4. mike Says: maybe transmission when it is cold it works but when hot it does not Tag: What is wrong with my car? Now and then won't keep RPM. If left alone for hour it fixes itself?