It's perfectly normal for the engine to idle down when you seal the PCV valve completely off. Since the PCV system is not closed, it is more or less a controlled vacuum leak. That's how it operates. See attached.
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This is the way the 426 hemis I had came from the factory. I tried it on my 505 wedge and it acted like a huge vacuum leak, pulled it back off and installed a breather on one side /pcv on the other, rpm went back to normal ! I aint got that figured out yet .
I tried a crankcase vacuum test on it w/ just the pcv valve on one side and a gauge on the other/sealed up, , idleing at 1100 , to about 3000 or so it had 4" of crankcase vacuum, and went up a small amount as I raised it a little more, didn`t go any farther , the engine wasnt warmed up. The intake vacuum runs about 9/10 at idle and 14/15 at cruise. Really wondering why I keep having oil leaks ----------anyone got an answer ????
