Code 25 engine lean

I would start with a fuel pressure check, low pressure could cause a lean condition. Next would be any exhaust leakage above the sensors (even a tight exhaust vale could let in enough to cause a problem).
Clean the AFM to be sure it is not sending the wrong data.
Check all of the wiring to the sensors, a bad signal wire will cause this code as the ECU substitutes a value if it does not get an actual signal from either sensor. The black is likely soot from oil burning as the engine has a lot of miles and wear.

Keep us in the loop.

It sounds like you are on the right track. Here are some engine wiring diagrams (below) and a guide to help you do some testing to confirm the problem.

https://www.2carpros.com/articles/how-to-check-wiring

I gave you both turbo and non turbo engines

Please let us know what happens and upload pictures or videos of the problem.

Cheers, Ken

How did you repair the O2 wiring? Some vehicles are VERY picky about sensor signal wiring, splicing a wire can introduce just enough resistance that the sensor works but falls just outside the proper range and you get a code.

Strip, clean, apply shrink tubing, twist wires axially, then solder, place shrink tubing over joint and shrink in place.
Simply twisting the wires = failure in a few minutes do to vibration and loss of contact.

Not the best video but it works.

https://www.youtube.com/watch?v=9ErNVJytyNs

O2 sensors are an interesting item. As a quick instructional, Early single wire sensors were platinum based and used the exhaust system as the return path for the sensors. They worked but you could get some strange readings if the exhaust rusted.

Next came the narrow band 3 and 4 wire zirconia/platinum types that start generating voltage at around 300 degrees F. And have heaters in them to get them operating faster. These "normal" zirconia type will run between.15 -.90 volts. Most generate around.45 -.50 at a "perfect" 14.7 :1 and will cycle high/low as they operate and the ECM uses that signal as proof the sensor is working and as the control input for fuel mix.

These evolved into the 5-6 wire wide band units used on some vehicles. These are VERY sensitive, They also operate differently. Instead of the wide swings in voltage they put out a relatively constant voltage and only swing up or down if the mix is badly controlled.

Then you have the Titanium dioxide based lambda sensors. (Commonly called an Air/Fuel sensor instead of an O2 sensor) These don't generate any voltage. Instead they act more like a thermistor in operation. These will be fed with a 5 volt reference source and the oxygen content of the exhaust changes the resistance that the reference signal is fed into. That changes the voltage the ECM reads as it's control signal. These don't show up as.1-.9 volts but instead they will show as 1.5 - 3.5 volts depending on the make and model vehicle they are on.

Your buggy runs a 4 wire zirconia/platinum sensor..34-.65 are on the lower end of the scale and could trip the system lean code because they are that low and not running closer to the normal range.
Low fuel pressure or a vacuum leak could cause that.

Factory test -
Connect the positive (+) tester probe of a voltmeter to terminal VF1 (for No.1) or VF2 (for No.2) of the data link connector (DLC1), and negative (-) tester probe to terminal E1.
Then follow the chart included.

HMM that would make it different. Didn't see anything about it being the turbo unit in the description. For some reason they used the older tech on the turbo than the non turbo.
Not a big difference though. The signal is just carried back through one wire and it use the exhaust pipe as a return. With the voltage numbers you have you might try grounding the sensors directly to the chassis.
Be careful not to seal the back of the O2 sensors. They actually bleed air into the housing to make the electrodes work. One side is in "clean" air while the other is in the exhaust stream. The difference between the oxygen contents of those samples generates the voltage in the sensors.

Eric used to have a pretty good channel until money from outside sponsors seemed to make him forget how he got there.
I watch a bunch of the auto folks, plus a lot of the technical sites, sometimes you pick up a trick or remember something you haven't used for a while. It's also nice to see others fight with the same issues at times, makes it feel a bit less "lonely".

Too me this sounds more like a MAF problem, have you tried to replace or clean it? Here are a couple of guides to help see what Im talking about.

https://www.2carpros.com/articles/how-to-replace-a-mass-air-flow-sensor-maf

and

https://www.2carpros.com/articles/mass-air-flow-service

If it has the mechanical kind I would see if the door moves freely. I have seen where the door pivot wheres out and the door drags inside the housing.

Please let us know what happens.

Cheers, Ken

Yeah if the O2 sensor signal sticks it will cause codes and poor running.