Toyota Repair: code 25 and 26, air fuel ratio, toyota corolla

Question
Hi Ted.
What would cause my 1995 toyota corolla 1.6 ltr. engine to give me a code 25 and 26?
It has been running rough for a while, but ran real rough especially when I came to a complete stop, like it wants to die out. It would stutter when I start accelerating.
I have been dealing with this problem for a while and the last thing I changed was the timing belt that you recommended. This still didn't do anything. This is the first time that I drove it and it gave me a fault indication. I have also changed almost all the sensors, changed all vacuum hoses, all parts in the ignition system from the coil to the plugs. I resealed my ehaust manifold, replaced idle air control, cleaned out throttle body and intake manifold. All of this still didn't fix the problem.
The only thing i haven't changed out is the ECU and cat converter.

Any help would be greatly appreciated

Thanks
Dave

Answer
The code 25/26 are oxygen sensor fault codes, they indicate an alternating rich/lean condition, in most cases the problem is not the oxygen sensor itself, it's reacting to an either rich or lean air fuel ratio which in most cases is due to an engine misfire, since all thos parts were replaced with no improvement I would do an engine compression test, let me know what the result is.