Crankcase Ventilation Systems: Operation: QUATTRO

On Quattro models, at idle speeds, the PCV valve is nearly closed so that most of the crankcase fumes flow through a restrictor to the air duct above the air sensor plate. As pressure in the intake rises the PCV valve opens and allows the crankcase fumes to flow directly to intake manifold. Under boost conditions, the PCV valve shuts and fumes are again routed to the air duct above the air sensor.