Check Engine light Code 25 & 26, please HELP!!

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I have a 91 NA, i brung the car to toyota dealer to check it out got code error of 25 and 26, these 2 code are not very persise. There are wide variety that can cause this, the tech said the best possable problem would be the water temp sensor. What do you guess think? or have had problems with these 2 codes.
I just got my o2 sensor replaced yesterday

code 25 = Air fuel ratio lean malfunction
code 26= Air fuel ration rich malfunction

This is very weird, both at the same time?

engine code info
http://www.mr2-tech.com/bgb/mechani.../efi_system.htm