IAC operating differently when started cold vs hot

[dokatd]

So first off I want to thank everyone in advance and appreciate everything I have learned so far being a lurker.

Now on for the problem. I have a custom GM EFI setup using a 1227747 with a G2 chip etc. I have managed to get it to run very well so far. The EFI system is very simple on this truck and does not run a VSS or EGR. I do however have an IAC. The unit I have is a custom part with a stepper motor. It works very well but I have one issue I can figure out so far and it's hard to search.

When end you first start the engine cold the IAC acts pretty normal. But after reaching temp and running for maybe 5min or so it is still largely open. You can tell dues to the rush of air sound. The idles is decent though. Now if you restart the truck once it's hot, the IAC will almost completely close and idle is pretty much spot on. The IAC is operating drastically different. The truck will continue to run like this until you go through a cool cycle again. Really it does not effect the drive or performance at all and idle is decent in both states. But the noise and the knowledge that it's not quite right bothers the heck out of me.

So what am I missing?

[lionelhutz]

I ran into the same problem. Never figured it because a cam lobe failed and I swapped the whole engine to port injection. I suspected the cold IAC would properly open to the cold start counts but then stick when the engine started and the ECM tried to close it. Then, once some heat was added it would begin to work without sticking. The stop-start cycle would re-sequence it so it was OK.

[dokatd]

Certainly won't discount the IAC getting stuck but mine is remote mounted so it does not see the same heat as a typical engine mounted unit. I feel like mine is not re-setting properly. Then the reset cycle on stop start gets it back where it should be. But it should be at zero when it starts cold.

[ony]

iac steps vs coolent temp.

[dokatd]

IAC vs coolant looks fine. Regardless the coolant temp doesn't change between shut down and restart. Shut down and restart is literally just key off and then back on.

[ony]

I am not running 7747 right now mine bit the dust. on it an the 288 I run now I would have to drive 8 to 12 miles at operating temp before it would idle at 600,the 7747 is worse about idling like you described than the 288. I lowered them iac steps vs coolent temp by 15-20 below 195 f and it helped slow the idle down faster.there is a mile per hour adjustment for idle that helped also. icant remember what it is. this is on a stock truck but you my try it on your conversion.