How to verify a good crankcase pressure?

[Avant Nate]

Forgive me if I'm wrong, but I'm going to assume you have an AEB engine, therefore no vent in the valve cover. So how could there be vacuum? My cap flutters a little bit, but nowhere as much as the video. But I don't know if that means anything is wrong.

[Davdraco1]

It's dancing because there is positive pressure in the crankcase and valve cover area. I imagine that's normal. I thought it was doing that when it was tight.