Well I have been having problems with my truck running rich. The check engine light came on and I deciphered the codes that were flashing. I am getting both a "rich" condition code (2-5) and a "lean" code (2-6). I had heard about the fuel injectors leaking when they get old which would cause the engine to run rich, but I am confused as to why I get the lean code as well.

 

Sounds more like an engine management problem because of the bouncing from lean to rich...ie a sensor.
Start looking at the AFM, TPS and O2 sensors.

 

I forgot to mention in this thread that I have replaced the O2 sensor a couple days ago.

 

was is a universal?
or a genuine toyota part?

 

1990 4 runner with a 3.0L V-6 check engine light on and finally ran the diagnostic test yesterday - reading both a 25 and 26 code.
I have not changed the 02 sensor. both codes kind of confused me.

no running problems / good idle and still getting about 225 miles to the tankful. I am watching this post though !!!!!!
208,000 on this fine looking truck and running strong ! I had the windshield replaced on Friday - installed for $200.00 and they came to my office to do it. What a difference WOW

 

Sounds like you guys have something in common.

 

ive been getting this same off and on code 25 and 26...rich and lean condition...anybody ever come up with an answer...all the threads in here seem to just dead end on this subject...by the way the 02 sensor is new ???

 

I had a "system too lean" code that I just got fixed....turns out my Mass Airflow Sensor went bad and I had to get it replaced. Maybe that has something to do with it?

 

I had the same codes after I replaced my O2 sensor. Recently I had a leaking injector (# 3) and replaced the o-rings on all injectors on that side. Haven't seen any codes since. Don't know what I altered during the tear-down/re-build other than the o-rings and gaskets on the fuel rail and t-body, but something worked. Note: before the O2 sensor replacement I frequently got a code 71 - EGR gas temp sensor, which was odd since I don't have an EGR gas temp sensor. Those were only installed on trucks sold in Cali. and mine was originally shipped to Oklahoma. The 71 code hasn't returned since the O2 sensor change.