It is more than likely the Idle Air Control Valve, IACV. This keeps the idle steady under load and when warming the engine up. It can be found on the intake manifold near the throttle body. You can test it for movement, as it is a solenoid, by removing it but keeping the electrical connection on, have someone start the scar and see if the plunger moves. Also, check for carbon depsoits cloging the ports that it opens and closes. They may need cleaning out.