To test a PCV valve:
1. Remove the valve from the engine and shake it. It should rattle freely. If it doesn’t make noise, it may be stuck open or closed.
2. Blow through the valve. Air should only flow one way. If you can blow through it both ways or not at all, the valve is faulty.
3. With the engine idling, disconnect the hose from the valve. If you hear a change in idle speed or quality, the valve is likely good. No change in idle indicates a stuck-open valve.