Long time listener, first time caller.
I have a odd issue that I figured I would ask the brain trust before I just started throwing parts at it.

First the history of the truck.
1994 4wd std cab 22RE manual. Owned for 2 years.
All maintenance performed since purchase, relevant or not.

• All fluids changed.
• Tune up (valve lash, spark plugs replaced, spark plug wires replaced, distributor replaced, air filter replaced)
• Timing chain replaced (and backdated to dual chain)
• Water pump replaced
• Oil pump replaced
• Injectors sent out and cleaned (not including the cold start injector)
• Intake cleaned
• New exhaust (manifold back)
• New o2 Sensor
• A/C reinstalled
• All vacuum lines replaced
• Fuel filter replaced

A dozen or so times over the last 2 years my truck will not start in the cold. It turns over but doesn't even attempt to start. If I wait a day I can walk up to it without touching it and it will start just fine. Also whenever it's cold (think freezing or below) or wet (heavy rain) there is a reasonable chance that it will stumble and buck between 2k to 4k ish rpm. When the stumble happens I can downshift to get it above 3.5 - 4k RPM and it runs fine. If I let it idle it is fine. Only on that middle RPM range is the bucking/fuel cut. This leads me to believe that although it feels like a fuel cut/starvation, it isn't the fuel pump because I can go WOT and so long as I get above that range it will run.

My guess?
The fact that this is very binary and not a slow deterioration leads me to electrical.
Either the AFM or TPS has a worn spot that acts up whenever moisture or cold is introduced?
Also my understanding is that is the RPM range that the ECU goes into closed loop, and I don't believe that is a coincidence.
I have done a quick resistance check on the AFM and is seemed fine ( although since this is intermittent.... Who knows?)

This is the last gremlin I need to fix. Any insight?

Thanks!

Edit: this issue has persisted through all of my maintenance, so shouldn't be anything I did to cause this....

 

Put a new fuel pump in it. I just had the same issue ,it idled good and WOT was good. I threw everything at it,plugs,wires cap fuel filter ect. and I checked the fuel pressure and it was well within specs at 36 psi.I left the gauge on it and drove several miles and it went down to 25psi. So I replaced the fuel pump and it runs perfect now.

 

Not that I don't believe you, it just seems odd that it would be the fuel pump if the issues mid throttle but clears up WOT, increasing fuel flow requirements and and all.
As parts go that's cheap and is likely needed to be replaced soon anyway. I just been avoiding it because I really don't want to fight the inevitable Midwest rust lol.
It will be a week or so before I can get around to replacing it. In the meantime if we assume that isn't it, any other culprits?

 

yeah, dont throw parts at it that aren't needed. if your pump is working, don't pull it and put in another, that's a waste of money. verify that the part has failed before replacing it.