Originally Posted by NSFW
Why? The PCV system pulls air from the turbo inlet (downstream of the MAF sensor), and vents that air into the intake manifold (downstream of the MAF sensor). If it's clogged, you'd just have more air going through the regular intake tract (turbo, IC, etc) and less air going through the motor, but either way the amount of air entering the cylinders should be the same as the amount of air that went past the MAF sensor.
Sorry I ment to say egr exhaust gas recalculation valve. I know stis don't have them does the wrx?
If the egr is not closing all the way, Inert gas is filling space that o2 should be filling.
xlsupreme you also need to tell us what kind of car you have,or did I miss it