O2 Sensor problem Need help!

[Curly1]

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

[Ford Man]

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.