[mr0077]

Nevermind, the PCV valve closes as much as it can (slight air flow) when there is high manifold vacuum (like at idle), and opens when the vacuum is low (like accelerating). The vacuum pulls it "closed" and the spring pushes it open when it can overcome the vacuum signal. That way, it has minimum effect on the fuel/air ratio at idle (assuming it is hooked to the plenum and not a runner) and works only at higher engine RPM. I agree with Clois, I think it is almost a must on a daily driver, and highly recommended on any street vehicle.