How can I cheak to see if my pcv valve bad. My car runs fine but has poor gass mileage.

I'd look at the FPR first. Pull the vacuum hose off with the engine running and look for fuel leaking out of the nipple. There should be none.

Where is the FPR.

On the fuel rail (firewall side).

The PCV should rattle when you shake it. But if it hasn't been changed in awhile, I would just replace it once you get the old one out. Also, when was the last time you changed the O2 Sensor?

I'm having the same problem with my car. The car now runs good because I changed the crankshaft sensor but it is poor on gas. I was told that my O2 sensor is bad too.

My questions is, does bad O2 sensor the reason for poor on gas?

Also, how do you change the O2 sensor?

The O2 could very well be the source of your poor fuel mileage. Especially if it has not been changed in quite awhile. Your vehicle might be a little different than mine but the O2 is usually located right behine the rear exhaust manifold on the exhaust pipe. There is this special tool for removing/installing the O2 Sensor so that you don't damage the wire when your installing the new sensor. It usually has a coating of anti-seize on the new sensor'* threads. Most people here recommend you stick with AC-Delco when you buy the replacement O2 Sensor

if ur car is sc it should be under the big peice of plastic over the sc, there is a black peice of metal that says pcv on it just take out the screws and the pcv is right under it