Q: Just how much does clogged-up PCV influence idle and running condition? I know excess crankcase pressure can blow the main seals, but barring that just how much does the PCV influence running condition?



Background:
With the slightly warmer weather, I finally started opening up the intake side of the engine in my 20-valve 1994 850 Sedan.

I got into this part of the engine to replace the knock sensors after a 1-4-3 code and a CEL. The engine runs nicely, but there are a variety of noises to be traced and sorted out - particularly at low idle.

What I found down there should come as no shock to anyone who has bought a Volvo from a non-Volvo person.

Utter filth on everything - old oil, dirt, grunge, crumbing wiring tubes, etc. Not a huge shock, but never a particularly welcome sight. The PCV Flame trap was ~90% clogged. There was caked up crud in the TB intake. The bottom of the oil box was 50% blocked by crud. The PVC hose itself had a kinked rigid piece of tubing silicon-ed inside the elbow on top of the oil box - sort of a half-assed MacGyver...

I also found x3 manifold bolts, x2 large flat injector seals, the screw for the throttle-spool cover, and some other stuff practically pasted to the block by the crud.

Reportedly, this engine was rebuilt back in 2009, seems they dropped half the hardware in the process.