The pcv valve shunts gasses and moisture from the combustion process back into the intake manifold. It is basically a spring valve, that allows flow at and above a certain positive crankcase pressure. The spring can become worn, deformed, or caked with residue. Then it may allow the loop to be open continuously, diluting the fuel air mixture with crap, and also lowering vacuum pressure.
On my 540s we have a ventilator plate pcv, which must be replaced, but on your's I think you can remove and clean it in a solvent.
I bet your intake manifold and injectors are a mess. I have used a product called Seafoam (do a search on this board as to how it is used). Use this method at you own risk (I do). I would do 8oz in the last 2 gallons of the tank, and another 8oz in the case. Do the dealio, then drive straight to the gas station like you friggen stole it (italian tune up) and fill up, and when you get home change the oil out. Put a little atf dex3+ (like a half quart) in the case when you refill and it'll help clean stuff up.
Have you gotten any codes?
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