The engine can't run without air. Properly, this should arrive via the throttle valve or the idle air valve, mainly. This way, it will also be metered via the fuel distributor, and the proper mixture will happen. If there is an air 'leak' elsewhere, metering will be incorrect, but the engine will usually still run, and faster. If the throttle is closing all the way and the idle air valve is not stuck open, then check the air hose plumbing.