Bad O2 Sensor?

[lucittm]

Does anyone know the symptoms of a bad O2 sensor? I know I am going about this backwards, but I am a bit perplexed.

The car was running fine, then it suddenly would not idle and it is running super rich. The inside of the tailpipe went from tan to black in a few days and my mileage has decreased. I can get the car to idle by backing out the air (idle) screw to the point where it almost falls out, so I know this is something unusual.

I have not changed fuels, adjusted the mixture, and it still runs strong on top.

Do I have a bad O2 sensor, I know I could disconnect it; but I am not sure what that does to the system in order to evaluate the over-rich problem.

Help!

Mark

[colo964]

I've driven with my O2 sensor unplugged. It has never given visible changes that it was rich and really didn't notice the mpg changing. I've messed with my idle air screw, too: also no noticable differences (I think that just fine tunes the monoxide).

Try unplugging it. If no changes, maybe you have a bad injector or plugs or a clogged cat pipe, temp sensor, knock sensor, the list goes on.....

[lucittm]

I unplugged the O2 sensor and there was not really much difference, the idle seemed a bit lower still but that could be the original symptom getting worse.

I am beginning to think about fuel head, WUR, and frequency valve. I have not adjusted anything. Do these things just "go bad" and when they do do they "go rich"?

Colo, I am running a cat bypass, and my 965 does not have a knock sensor. I would think a clogged injector would cause a lean condition if the gas can't get through. My condition is rich.

I will have an AFR sensor installed this weekend and then I can report back with some numbers.

Thanks for any more ideas you folks might have.

Mark

[colo964]

I wasn't thinking clogged injectors. I was thinking somehow it is stuck open or something, so you are getting poor atomization and fuel dripping in all the time. Again, I'm guessing at this point.

I should have read the fine print that you have a turbo. I have no experience with those.