I've got my 350TBI with a 454 throttle body on an edelbrock 2" manifold, IAC and TPS are hooked up properly (wires traced back to the proper ports on the computer as determined by wiring diagrams). The car sat for awhile, so after changing the oil and reinstalling the battery, swapping out fuel, etc. I fire it up.

*cranking* Vroom.

Bitchin.

The only problem is that I'm idling at about 1400 RPM. I figure, great, it's probably the timing. So I get in there, monkey with it and set the timing to 6* BTDC with the ALDL wire disconnected and the diagnostic port jumpered from A to B. Cool. Reconnect the wire and now I'm at 1700RPM... some idle.

I think the ECM just isn't used to having that much air/fuel. The fact that the throttle body was made for a 454 truck probably doesn't help either. In any case, how can I tweak my idle so it isn't so rediculously high?

 

Turns out my IAC wiring WAS in fact done correctly... for a car that originally came with a 350, mine originally came with a 305. So, here's what I did:

I checked the TPS voltage, 0.540VDC.
Sweet.

I pulled out the IAC valve, key off, jumpered the ALDL connector under the dash and watched the IAC pintle to go flying off... no such luck, it just cranked down even harder into the OPEN position.
Not so cool.

Did a little checking and it turns out that on 350 equipped vehicles (e.g. Trucks) the IAC wires that go into ports A & B on the IAC connector are reversed from the way it is on 305s and 454s. Good goin' GM, way to confuse the aftermarket . Amazing what a little polarity will do.

Quick snip here, snap there, strip the wires, butt connector, check to make sure the pintle flies off, reassemble the valve, done.
Awesome.

Remove the ALDL jumper and *crankity-crank* vroomity-vroom, life is good with an idle down around 650RPM.

Hope if anyone else has a problem sticking a 454 TB on a 350 engine in a 305 car, they find this article.