1999 Chevy Lumina PCV valve

A bad pcv valve can cause serious damage to your engine; if you feel like it's gone bad, replace it; it's very cheap and it takes 1 minute.
With engine off, unplug the valve and shake it: it should rattle. If it doesn't, replace it.
With engine on, unplug the valve: you should feel a vacuum at the valve: if you don't, replace it.
If you're not sure: replace it (again, it's very cheap and easy).