I'm new here so if I've violated a rule by posting forgive me. I have a 96 Tacoma 2.4 sporadic stalling with p0171 code. I have changed mass air flow, fuel pump and strainer, fuel regulator, fuel filter. Plugs wires cap and button. It may stall first thing in the morning in first gear or running 65 mph after 50 miles. It might not do it for 2 or 3 days or 4 times on the way home.. I'm at my wits end and tired of throwing parts at it.. The temp sending unit harness is damaged. Sometines I have temp reading sometimes not. I have yet to find a replacement harness (it's a one wire). Any suggestions?? Please..

 

Symptoms and code suggest an intake or vacuum leak. There are a few ways to test for that, the best being a smoke machine. You might Search for other methods (unlit torch, friend with bong...)

 

Smoke completed, no leaks. Sorry i didnt mention that in original post. Today i changed temp sensor and harness. Still stalls.

 

Can you elaborate on the stalling? Does it do it when the engine is at idle, or at higher RPM's? In gear and under load? How's it run and idle otherwise? Any smoke? Fuel consumption?

P0171 means your engine is running lean, if not all the time, then long enough to throw the code. That means either too much air or not enough fuel. The former means intake leaks, but your smoke test appears to have ruled that out... The latter is either a fuel delivery problem, or injection problem. You already replaced the pump, filter, and strainer, so other than clogged supply lines, we're left with injection issues: clogged injectors and electrical problems. How'd the temp sensor harness get damaged, and is it possible other wires are damaged as well?

For now, I'm out of other ideas. Do you have access to a scanner that can do datalogging?

 

Try to answer all your questions. It will stall at any time in any gear at all temps. Gas mileage same. Runs perfect otherwise. I do not have access to diagnostic machine. 3 different code readers have been used. I dont know how temp sensor got damaged. Assume plastic became brittle from age..fortunately it being a 5 spd when it stalls at cruise it will usually catch itself right back up.. Thanks for your time and attention.

 

Sounds like fuel issues, then. My next step would be to come up with a datalogging scanner, drive around, and observe various fuel parameters normally and when it stalls: fuel pressure, injection quantity, maybe others.

 

Having thought about this some more, if it's stalling suddenly and briefly, and picking right back up, that suggests your problem is more likely software (wiring), not hardware. Either way, the best next step is to datalog while driving. Or you could just start checking various wires, starting with grounds.