I would try replacing the idle air control valve. i had the same type of thing happen on my gt stang. If not try adjusting the idle control screw, should be by the throttle body. When adjust your idle screw, unplug your idle air control valve. If its adjusted right it should almost stall out, or idle very low, like 500 rpms. if its still idling high, adjust the idle screw till your car almost dies when the idle control valve is unplugged and when you plug in your idle air control valve it should bring the rpms up again to normal, hope this help you out.