squirrelly gas mileage... need O2 sensor?
 

Okay so I decided to test my gas mileage for the first time in a few months, and I am used to getting about 35-37 mpg on my civic. I measure it in a pretty standard way, just fill the tank all the way up, reset the tripometer in the car, then take note of how many gallons I can fit in the tank on my next fill up. Then I just divide the numer of miles by the number of gallons I used up, easy enough right? Well this has always yielded consistent results, but this time it was crazy. I got 50 mpg on the first tank, that was 250 miles on only 5 gallons. I couldn't believe it. So then I measured on the next tank, but I only got like 42 mpg. Then I kept measuring it after that and got as low as 25 mpg once, and recently all of my fillups have yielded about 37 mpg. All of my unique measurements were done on highway driving, and the temperature was about the same outside each day. The only things I have changed on my car are my exhaust and some lighter than stock alloy wheels. Is it possible that I need an 02 sensor, since some of my readings were kind of low? Is it possible to get abnormally high gas mileage from a bad 02 sensor? I dunno what to do, I've never seen my mileqage fluctuate so much.

Re:squirrelly gas mileage... need O2 sensor?
 

Well, i dunno, but im almost positive my 02 is bad right now, and it even runs rich at idle, so my gas mileage is suffering quite a bit. I would just look at the basics like a clogged filter or something like that first.