The throttle plate should be fully closed, the IAC controlls idle speed.
A tang on the throttle shaft will hit the the throttle body casting when it is closed. Usually there is a throttle stop screw to adjust. On units without a throttle stop screw, bend the tang to allow the plate to close.
You must remove the intake hose so you can see the plate.
Not too far or the return spring pressure can cause the throttle plate to dig into the wall.
