So a couple of weeks ago my D1 started high idle one morning. No biggie, I'll take the other car to work and clean the TB and IACV that weekend and itll probably be just fine. Pulled everything apart, cleaned the gunk, was careful to not move the IACV, put it all back together and had the same issue. Luckily I'm friends with a local indie and he was able to swing by, reset it, and it started idling just fine.

I didnt think much of it, left for a week, then today when I came back it starts and idles okay, albeit a touch low, but absolutely falls on it's face if you try to drive it. I limped it back around the block and confirmed that itll idle (around 700-750 now) but any throttle causes it to miss like crazy.... UNTIL the AC is turned on, then it runs like it should.

That last part has me a bit stumped. I checked my fuel pressure and it's good, new plugs and wires were done maybe 2k ago, air filter is new, and nothing else had changed. No codes are being thrown.

 

do you know what your mechanic did to "reset" it ?
turning on the a/c will send signal to the IACV to increase the idle speed to compensate for the extra load on the engine

 

He used autologic to reset the adaptives is what he told me. It was maybe a 5 minute thing. Normally would have stayed and had a beer, but needed to run.

Only thing that is bugging me is the fact it runs absolutely perfect with the AC on. I took it for a very short cruise around the neighborhood to confirm and it's as smooth as it has ever been until the AC is turned off. Once you turn it off now itll fall on its face and die.

 

the following things come to mind,.... throttle position sensor, wiring to the sensor and wiring to the iacv. You have a '96, but do you know if your truck is "Advanced Evap " or not....it will tell ioon the decal by the radiator, and the advanced evap canister is more rectangle shape than round ( roverparts.com has a good description)
I had an issue with the fuel tank pressure sensor ( or circuit to it) failing and taking out the TPS with it since they share some of the same circuit...on the advanced evap models

 

Advanced Evap wasn't a player until mid 97. See if your buddy can adjust the base idle with his AutoLogic.......

ENGINE TUNING

Service repair no - 19.22.13

The position of the Idle Air Control (IAC) valve can be

checked using TestBook and adjusted if necessary

through the by-pass screw in the plenum chamber.

The bypass screw is covered by a tamper proof plug

which can be extracted using a self tapping screw.

All vehicles:

1. Ensure air conditioning and all electical loads are

off. Vehicle must be in neutral or park with air

suspension in kneel and disabled.

2. Carry out tuning or base idle setting procedure

as applicable using TestBook.