front O2 sensor problem.

Hi. i'm having a problem with my car. First off, it's a 2002 2.2L Pontiac Sunfire with 29,000km. About a month ago, my check engine light went on, so I brought it to a mechanic I knew and he checked it. It was the O2 sensor in front of the catalytic converter. He looked at the numbers it was giving out, and they ranged from 100 to 700 i believe it was, changing randomly. For example being 141, 693, 200, 700, 329.... So he cleared it and told me it could have just been bad gas so to just drive it until it was nearly empty and then put premium. It went on before the new tank of gas, then went out once premium was put it. It then never appeared during the whole tank of premium gas. Now I just filled with regular gas again about 2 weeks ago, and it just went on again at around half a tank. Why wouldn't it have gone on with the premium? Was it just luck. He told me that i would need to change it if it kept coming back on or else my fuel economy would go down and well wouldn't pass an inspection. He still can't believe that the sensor is acting up seeing how the car has no mileage on it at all. Any ideas on how I can fix this without changing the sensor? If there's no choice, what kind of sensor would you suggest? Any help would be great. Thanks

Its quite possible actually. Your car may have very little miles or kilometers in your case. But its still almost 5 years old. Parts deteriorate over time. Like hoses and other seals do. Your front O2 sensor is the most important. So replace that with a factory Ac delco one. Bosch are pure junk and will most likely not work since i have seen it happen in j-body's before. If that dosn't cure your bad gas milage start looking for a vacuum leak. I found a nice slash in one of my vacuum lines which controlled the vent controls inside the car and that was killing my milage. G'luck.

Doesnt sound to me like it was acting up by the reading he got. The front O2 should register it sweeping back and forth. If you had an A/F gauge you'd know that, because once it's in closed loop, it'll just sit there and swing back and forth from rich to lean, all day long. The ECU actually can make adjustments that fast.

You sure it wasnt a code for a slow response from that front O2 sensor? I've had that before.... just something that would periodically come on and go away.

I dont believe it was a code for a slow response, however i'm not entirely sure. The gas mileage hasn't changed yet, my mechanic just said that it probably would since it doesn't monitor it once it's in the closed loop. I supose i'll just have it changed. Thanks for the help guys.

This might sound obvious but when you went back to regular gas after the premium test, did you get it at the same gas station where the problem started? If you went back to the same station, you have what could be the answer.

Hi. No i haven't returned to the same gas station as the first time. I got regular at another gas station, and since the light came back on when my tank was nearly empty, I put premium back in, and guess what, it went out after driving around 60km. I supose i'll just need to have it changed if it acts like this. Some people told me that it might just be luck that it leaves when I put premium, but it's twice now that it works. I'm at about half a tank and all is looking good up to now...