replace thew valve and probably the hose it's connected to.
Check and clean the "pot scrubber" inside the oil filler cap. This is where the fresh air is drawn into the crankcase for the pcv system. You can do this by soaking it in kerosene or gasoline. Get all the crud out, let it dry and moisten it witha small amount of clean fresh oil.
While you're at it, check and/or replace ALL of the vacuum lines on the car - including windshield washers, etc. Cracked leaky vacuum lines can cause all sorts of rough running trouble.
I think it also goes without saying to make sure your plugs, wires, points, cap, rotor, etc. are all in perfect shape and within specs. Change your oil too if need be.