i went ahead and replaced mine. could someone please explaine to me what's it's supposed to do?

 

PCV positive crankcase ventilation. its mounted in the valve cover and connected by hose to the intake manifold. it sucks oil and gas fumes from the crankcase, eliminating any pressure buildup that might be caused by piston ring or valve guide bypass. it also reburns those fumes, instead of venting them to the outside.

edit... whats the difference in a good one and a bad one. a good one will rattle when you shake it with the little ball moving freely. a bad one that doesn't rattle is either stuck shut (no vent) or stuck wide open (too much vac leak)

 

thank you. my old one was still good then.but heck it was only 4 dollars to replace.