I am currently getting very poor gas milage at idle and not so bad but poor highway milage. My 02 sensor works fine, but I found that I had a small leak in my exhaust manifold. Try checking yours for leaks while it's running, it could fix your gas milage problem. The o2 sensor in my car is at the bottom of my exhaust manifold and this is why I thought my 02 sensor was not working and wasted 75.00 to get a electronic engine alalysis done. Just to tell me that I had a crack in the exhaust manifold.
Good luck
lever_John@hotmail.com
91 ford mustang 2.3 Litre 4 Cylinder