Before you do anything, try this:
Remove the Idle Air Control solenoid and clean it out thurougly with brake cleaner, carb cleaner, or whatever else you got. Make sure that you detach the actuating motor before you do this, so that you won't damage it, and so that you can tell when the plunger begins to move freely. If you don't know where the IAC is, it's a cylindrical assembly that is attached to the upper intake plenum.
Also, make sure that the two air conduates to and from the IAC solenoid aren't gunked up.
If this doesn't work, you need to start diagnosing the problem by using a EEC code reader, which you can purchase at almost any auto store, or department store with an auto section. Wal-Mart (aka Satan) sells it for $30.
You might also try setting the base idle. However, this will also ***** with the throttle position sensor calibration. If you want to set the idle anyway, disconect the electrical connector from the IAC solenoid. Start the engine up, and adjust the throttle plate ***** until the engine idles at 650RPM. TUrn off the engine, and plug the IAC back in. You might also want to reset the computer by unplugging the battery, so that the computer re-learns the idle curve.
