PVC valve

[old1k]

Whats the theory of operation on the PVC valve on the 230 engine? Was thinking at high vacuum, the valve would close or restrict air flow and at low vacuum it would open and suck through the crankcase. Factory unit on there, only closes at hi intake prressure,???? there is no seat inside the valve for the needle to sit against and close . Am I missing something here or what?

My main problem is bad idle, lif I plug the valve at the manifold it runs great. No amount of carb adjustment will make it idle smooth with the valve in the curcuit. Timing is good ignition system is good, just need to know how this vent system operates

[moosejr]

The intent of the PCV valve is to vent the crankcase into the intake airstream rather than have any blow-by just excape out a vent. You have a vent port bringing filtered air into the crankcase, the pcv valve allows manifold vacuum to suck out the pressure in the crankcase, without letting the air-fuel mixture in the intake manifold pressurizing the crankcase, and also bringing in combustible gases into the crankcase. Essentially the PCV valve is a one-way valve, . air flows FROM the crankcase TO the intake manifold, without creating a vacuum leak. Your symptoms sound like the valve is partially plugged with sludge, preventing it from moving freely and sealing when it should. A good general test is to pull the valve out of the valve cover and see if you hear a hissing sound, if plugging off the valve resolves your idle issue, replace the valve. Just because you can shake the valve and hear it rattle doesn't mean it is working correctly.