I'm checking the valve in my Explorer while the manifold is off to change the plugs and the valve is easier to get to. I have it out and it rattles fine when I shake it. I can suck on the vacuum hose end of it without effort. I can also blow into it with only little resistance. Isn't it a one way valve so I shouldn't be able to blow into it at all? Be that as it may, does that even matter, as I can't see a time when that would be important as there is always some vacuum on it. It's not a turbo engine.