For the last 3 weeks my MPG has been dropping. I was getting 42-43 and consistently, but it dropped down to 34-35. Well on Monday i unplugged my o2 sensor in front of the cat and my MPg jumped up to 40, I have a scangauge. The scangauge has xgauge and i plugged in the code for the o2 sensor, it was reading anything from 0-97 when it was plugged in and 127 unplgged. It didn't make any difference how i drive on the reading of the o2 gauge, it just kind jumped around. I never got a check engine light. Would the o2 sensor make the MPG drop or some other sensor cause the car isn't going into a closed loop. Also would it hurt anything on the car have the o2 unplugged? I have a 03 civic 5 speed 97k.