O2 Sensor problem Need help!
 

I have an 08 Chevy HHR with the 2.2 Ecotoec engine. I love it and have made a bunch of changes to improve mileage. Now I have run into a problem and hope someone here can help. My mileage has been down some latetly. Did a data log on it and it shows fuel trims on the lean side so the ECU is adding additional fuel and hurting mileage some. The O2 sensors says it is a little lean. The car only has 25,000 miles so I would think the O2 sensor is still good.

Any suggestions on how to correct the problem?
Thanks in advance. Curly

The 02 sensors should still be good. Usually if an 02 sensor goes bad it will have a drastic effect on FE, usually causing a 25-35% drop. If the 02 sensor is bad you also should have a CEL. The plugs should still be in good condition, but you might want to pull them out take a look at them, clean them and regap them.