Setting TBI base idle (IAC)

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rob249

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Truck is a 94' Yukon, TBI. Recently rebuilt/resealed the TBI, and put in a new distributor and set timing.

At the beginning of this summer, I tried raising the idle a little bit for more AC performance, not realizing that the IAC would just bring the idle back down. Now Im trying to correctly reset the Idle screw.

I turned the key on with a paper clip inserted into the A and B terminal, but didnt start, waited for 30 seconds and unplugged the IAC. I then started the truck and attempted to reset the idle rpm to 650, problem is, the rpm immediately shot up to 1600. Backing the screw all the way out only bought it down to 1200rpm.

Do I remove the A and B jumper before starting? Maybe I have to unplug the timing advance?

Clearly Im missing something here. Figured Id come to the experts before I attempt it again.
 

BeXtreme

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Do you have an ALDL scanner?

Did you make sure the engine was fully warmed up before you started doing this?

You jump A and B(white and black wires) and then turn the key to "ON". Make sure it is not just accessory, but ON which should be the stop right before start.

Wait 10 seconds and then unplug the IAC.

Turn key off.

Remove jumper.

Start engine and let it settle into the idle.

Adjust idle to around 600RPM.

Shut down and reconnect IAC plug

Start engine and let it run for around 5 seconds.

Shut off and let sit for at least 30 seconds.

Done
 

rob249

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Truck was at operating temp. Dont have a scanner, truck does have oem tach. I didn't remove the jumper before starting, that's probably it. Im guessing jumping A and B disables several things. Thanks
 

PlayingWithTBI

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I didn't remove the jumper before starting, that's probably it. Im guessing jumping A and B disables several things
Here's the procedure (in .pdf form) for setting your base idle and TPS. It's old but works on our trucks too.

Another way to do it, with a scanner. Start it up like normal, warmed up, with A/C off. Adjust your min idle screw until you see the IAC ~10+ steps.
 

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rob249

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It was definitely the jumper still being in. I pulled the jumper out after pulling the IAC plug and before turning the the key off and restarting, that runs the rpms up. If you turn the key off, then pull out the jumper, then restart it works. Thanks all.
 

PlayingWithTBI

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PlayinWithTBI to the rescue again
Thanks man! Hey, you coming to Dino's Git Down?
 

rob249

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Cant unfortunately, still have some work to do before my roadtrip. How big is that car show?
 
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