Unburned fuel blowing out the exhaust
I just failed my emissions test. The computer showed an O2 Sensor error. I just replaced an idle air control valve last week and thought that was the final issue. The Check Engine light is still on too. The guy at the emissions testing facility (Littleton, CO) said I'm blowing unburned fuel out the exhaust which I had suspected but the repair shop (Pep Boys) denied that was happening. I noticed my gas mileage dive sharply from the 17/18mpg I was getting, down to 15mpg I get now. No noticeable loss of power though. Can this really be caused by an O2 sensor? Or is it possible I have a spark plug not firing, or valve adjustment problems? Thanks for any help some one can offer!
Cars & Trucks - Isuzu - Rodeo - 1999 Isuzu Rodeo
Answers & Comments
Yes, that can be caused by an O2 sensor.
Valves, fouled plugs, etc., would usually cause "missing", not necessarily rich mixture.
No exhaust leaks -- I would next suspect vacuum leaks or the Mass Air Flow Sensor (MAF) is not functioniing properly because of bad seals or failed electronic components in the MAF.
Charlie
Re vacuum leaks: some would cause a lack of power and some not so much -- it's difficult to say for sure.
Charlie