Can someone tell me, or show me with a diagram or photo, where the PVC valve is located on a 1991 Civic engine? Thanks.

 

I think you mean PCV...

right behind the valve cover, on the runners of the intake manifold...a little plastic tube bent at 90°.

 

It will help you to go to a local auto parts place and buy a new one (less than $5) to replace the old one. That way you'll know what you are looking for. A new one can really help make the car run smoother if it hasnt been replaced since 91.

 

I bought a new valve, plastic piece at 90 degree angle.

Looked where you said (also where I thought it should be) cannot find similar piece to replace. There is a straight threaded fitting (looks newer) screwed into runners and connected to hose on top. ?????? Am I still looking in the wrong place?