The PCV provides a one way exit for gasses built up in the crankcase. Over time, contamination might cause reduced air flow and cracks can occur in the housing. This assembly also includes the oil separator, which allows the crankcase to safely vent air and stop oil from escaping during the process. If your car is experiencing a loss of pressure or a decrease in performance with a rough idle, this valve/oil separator might to be blame. If the crankcase is unable to vent the air, pressure can build up and weak seals may start to fail. This valve sits in the engine valley, beneath the supercharger compressor.