Positive Crankcase Ventilation
WARNING: This page is about a different car, the 2003 Pontiac Grand Prix, 2003 Chevrolet Malibu, and 2003 Buick Century. However, it is still accessible from the selected car via links, so may be relevant.
The Positive Crankcase Ventilation (PCV) system is used to consume crankcase vapors in the combustion process instead of venting them to atmosphere. Fresh air from the throttle body is supplied to the crankcase, mixed with blow by gases and then passed through a PCV valve into the intake manifold. See Fig 1 .
The primary control is through the PCV valve which meters the flow at a rate depending on inlet vacuum. To maintain idle quality, the PCV valve restricts the flow when inlet vacuum is high. If abnormal operating conditions arise, the system is designed to allow excessive amounts of blow by gases to back flow through the crankcase vent into the throttle body to be consumed by normal combustion.