Normaly the Idle control valve will stick open gummed up with carbon. I believe you have an electronic idle control system. Take the control valve out and clean with carborator cleaner. If you are able check the function of the valve by shorting 12 v battery power across the valve electrical terminals. The valve should move from open to closed position with a audible click. Reinstall and hope for the best. If cleaning does not work measure the voltage at the valve. You should get around 5 volts on one side and ground on the other. If not check the fuses and wires over to the idle control computer. Sometimes a fuse or power supply is the only problem other times a wire goes bad. Good luck. John