How do you know if your O2 sensor is bad? Right now when my car idles the econogauge sits about a quarter of the way in from the left side. Is that normal? I am still getting around 20mpg from the car, and that is what I was getting when I purchased it. I however don't remeber the econogauge sitting like that, I remeber it sitting all the way to the left at idle.

Is there something wrong? or am I creating problems in my head.