I don't believe my 02 sensor has ever been changed. When i had a valve job done, the fuel mixture was way off. I got in back to about where it should be by feel. I know this is not the proper way to do this, but it had to do for the time being, and it seems pretty decent (before this it would hardly accelerate).

My question is, if the 02 sensor regulates the fuel/air ratio, then should I have not been able to adjust this?

One more bit of information: the car accelerates much better before it is up to operating temp, then once it is warmed up, the engine does not feel as strong. The O2 sensoe does not play a part until the engine is at operating temperature, correct? This would lead me to believe that it is not funtioning properly.

Any thoughts on this would be greatly appreciated.
Mike