Ok, Im not arguing with you Bill, just saying what happened. All he said was he replaced the 02, and the car started feeling a lot better. He could of replaced something else, but didnt charge me. It threw two codes, and wouldnt accelerate as good, until it was fixed. I replaced my front 02 two months ago, and did not feel any improvement, but I really wasnt expecting any.

Hmmmm....what are the odds he replaced the front O2 again? Have you read DrJay'* comments on 'lazy' or 'weak' O2'* out of the box?

Well if my input is worth anything... Short and sweet, the rear o2 sensor is only used to determine if the catalytic converter is functioning properly. I'm looking a bit more into a few "little known" things about the PCM and it though, which might explain some of what you say you experienced. I'll post later though.

I dont think so, because I had my front 02 in there ever since I bought the car. Because a little while after he fixed the rear 02 I did a tune up and replaced the front 02. It was rusted in there pretty good and scuffed up my hand very nicely also.

Well I'll share what I've learned so far, and it may explain what you're experiencing. Although there is no proof this applies to our cars and you may still be having an 'assumed' increase in performance or somthing else was a factor.

That said, the international Automotive Technicians' Network (iATN) has "proven" that if the front o2 sensor fails the PCM may revert to the rear o2 sensor and provide wrong information to the PCM as a result. The PCM basically figures its better than nothing. Since catalytic converter health is a big factor in the reading there is no correction factor used.

The problem is it may not revert back to the front o2 sensor even after its been replaced! This would require resetting the PCM. The iATN suggests hooking an exhaust analyser to it so you can determine if it is infact off.

I'm curious if you can hook a scantool up, keep a close eye on the readings, then have a buddy disconnect the rear o2 sensor and determine it by that. If there is no dramatic change you should be able to assume its not reading it...come to think of it, if it still gets a reading at all after disconnecting the front you know its reading the rear...or it may be displaying the front o2 value but not considering it when determining a/f...Anyway as you can see there'* still a lot of research to be done.

*slides out the back door*

hmmmm, anyother way to fix it would be to just unplug your battery overnight after you have them worked on, right?