A couple of weeks ago, I changed the o2 sensor and pcv valve on my car. (98 grand prix se, 3.8l n/a, 191,000 miles) Before this, I was getting about 19.5 miles to the gallon. I filled up yesterday, and I am getting 16.5 miles to the gallon. I reset my trip odometer every time I buy gas, and by comparing that to my fuel gauge, it looks like my mileage is falling even further. I made sure that it was screwed in all the way, and that the plug was seated correctly, and everything looks fine. I was going to put the old sensor back in to see if that fixes it, but I went and checked the garage where I left it, and someone threw the old sensor away. Any help?
