1999 engine behavior diagnostic help wanted

since starting on the "simple" misfire hunt I replaced the plugs, the injectors, the maf sensor and the two O2 sensors. and he passed a compression test. sensor 1 responded with some short term fuel trims, i think. maf sensor is giving correct temperatures, same as cooling water and trans oil temps, ambient when engine hasn't run.

still, when engine warms and the tach heads down toward idle, a miss develops and increases, engine moving in the mounts type of miss. getting Bank 1 lean codes.

BUT, I pulled off the intake piping and ran it without the intake air sensor the engine stopped it's missing around and sat idling like a normal engine. running rich because no input from sensor 1 or the intake air. can't run it that way. but when I get the lean codes fixed it runs too rich to run.

i tested for vacuum leaks with propane. never changed rpm, so if it's vacuum I missed it.

i don't have a number for the fuel pressure, but the pump works somewhat because it pressurizes the fuel tank. and spins the engine.

it seems to me the suspects could include a wiring problem or a connector issue, or another sensor that I am not aware of. yet.

it doesn't idle when it sees sensor 1 and the maf sensor, but it idles when it doesn't see those, but too rich.
what other sensor figures into the mixture control? I'd sure like to find that out?

any ideas or better, anyone who has already solved this problem with a 1999 SR5 V6 4WD AUTO TRANS 4RUNNER?

THANKS

 

I got runner running right recently, and finally got him to a minute clinic where the scanner man announced that he passed all tests and diagnostics AND that it's a strong engine. Then he agreed to put the rest of the stuff in for a few hours of labor time, water pump, timing belt, radiator, trans cooler, LBJs, stuff like that. meanwhile I am refreshing the gearbox fluids, will drop the trans pan and clean it out. flush out the brake lines. and start packing for the summertime special road trip.

muchas gracias for all the assistance and knowledge base help. another stricken 4Runner heading down the highway

 

Congrats!!!

 

So what was the cause of the misfire?

 

2 years later...and the mystery continues.