1994 code 25 cry for help!

[SKULLGRINDER]

Preface; truck is a 1994 OBD1 truck all stock no weird parts going on. PAIR system removed and EGR bypassed the correct way. Often times the CEL is on for a code 25. Which reads air fuel mixture lean. I have ran through the basics of the FSM diagnostic to include the following.
NEW OEM o2 sensors ( 93-94 correct p#)
NEW OEM spark plugs, wires, distributor cap and rotor
Bench tested AFM and replaced with lower mile unit ( passed test)
NEW OEM intake pipe
Checked for vacuum leaks
Good fuel pressure to include new fuel filter
inspected harness around EGR ( no damage)
engine ground bolt secured
After running through these items the trucks still persists on the code. Symptoms include rough cold idle. Super lumpy and wants to die if you do not give throttle. Feels like a slight miss at lower RPM and down on power. The light will intermittently come on and off while out for hours in 4low on the trail but constantly on when driving on the road. Once warm truck seems to run alright for what it is however I feel like I am leaving some power on the table. Not usually anal about the CEL but the lack of power makes me want to address this issue. What makes me think it's down on power? When the ECM is reset and the truck is in "closed loop" it seems to idle well and have a little more power and throttle response. Any insight or similar experiences would be appreciated. Thanks!

 

[jonheld]

Codes 25, 26, 28 scream O2 sensors or associated wiring.
After replacing sensors, I'd be checking for wiring/connector issues.

 

[Wayneraintree]

I had previously replaced the O2 sensors in the lower factory spot on my 94. I kept getting the same CEL as you with erratic idle. I replaced the semi new O2 sensors with Part Number: 89465-69115 and placed them in the PAIR location on the exhaust manifold, and it solved my problem.

Check the gaskets between the exhaust manifold and downpipe. If they are deteriorated and air is getting in upstream of your O2 sensors then that can cause problems.

 

[SKULLGRINDER]

I had previously replaced the O2 sensors in the lower factory spot on my 94. I kept getting the same CEL as you with erratic idle. I replaced the semi new O2 sensors with Part Number: 89465-69115 and placed them in the PAIR location on the exhaust manifold, and it solved my problem.

Check the gaskets between the exhaust manifold and downpipe. If they are deteriorated and air is getting in upstream of your O2 sensors then that can cause problems.

How/where did you fish the harness from to bring both o2 harness pig tails up to the PAIR system holes?

 

[Wayneraintree]

How/where did you fish the harness from to bring both o2 harness pig tails up to the PAIR system holes?

How/where did you fish the harness from to bring both o2 harness pig tails up to the PAIR system holes?

That part number has long enough wires that it reached both leads on the harness and the connectors are an exact match.

 

[hisandhers80s]

The wires to the O2 sensors pull up the firewall from the exhaust location to the exhaust where the Pair was connected.

 

[SKULLGRINDER]

The saga continues. Chased both wiring harness ends all the up into the engine bay. Refreshed with new OEM pins and connectors as well as moved my sensors to the manifold. Cleared the code and truck seemed to run great. Fast track to today code 25 pops again. Double checked my work I have 12V on the yellow red 1V on black and yellow .7V on blue and white and .007 on grey. All within spec from what I’ve read. At this point I don’t know what else to do. FSM scream code 25 (lean) is o2 related yet all my tests come back good. Some have suggested exhaust leaks and or vaccum leaks. From what I can hear and see I don’t have any of those either.

 

[jonheld]

The saga continues. Chased both wiring harness ends all the up into the engine bay. Refreshed with new OEM pins and connectors as well as moved my sensors to the manifold. Cleared the code and truck seemed to run great. Fast track to today code 25 pops again. Double checked my work I have 12V on the yellow red 1V on black and yellow .7V on blue and white and .007 on grey. All within spec from what I’ve read. At this point I don’t know what else to do. FSM scream code 25 (lean) is o2 related yet all my tests come back good. Some have suggested exhaust leaks and or vaccum leaks. From what I can hear and see I don’t have any of those either.

Make sure the ECU is getting those voltages from the O2 sensors.