my 91 gt is still fuel injected but the problem im having is it idles up and down for bout 5 min then the idle smooths out for another 3 min and after will gradually start idling higher and higher on its own up to around 2 g's im not real sure wat is causing this but im leaning towards the tps sensor if anyone knows wat it is or has an idea please let me know

 

fuel pump... distro .. leak in vaccum

 

Idle Air Control (IAC) valve. Take it off and clean it with some carb cleaner, reinstall. Would also clean the throttle body while your in there. If that doesn't fix the problem, then replace the IAC valve. Search the forum or the internets for instructions on how to clean an IAC valve.

If your handy with a multi-meter: disconnect the IAC valve's electrical plug and make sure that the connector pins on the IAC valve have between 8 and 14 ohms of resistance. Any more or less and the IAC valve needs to be replaced. Also make sure that neither pin has continuity with the body of the IAC valve.

Good luck...

 

idle air control valve, and if it has mass air check that two, unplug mass air and see how it runs without it.