I'm working with a ZZ4 with a Comp 276 roller, Sportsman II heads, 454 TBI with 90pph injectors run by a 7747 ECM.

The IAC will always max out when you take it out of park/nuetral. We've tried opening up the throttle plates really far and it has no effect. I've tried setting the max IAC to 235 and it still opens it all the way to 235. It seems like the IAC is having NO effect on the idle.

I've checked the wiring and I've pulled the IAC to see if it is operating. It goes to zero when you jump A and B on the ALDL, and it goes to the middle when you turn the key on (should be 130 counts).

I'm out of ideas????

 

Grumpy...Glenn...Trax??

 

Whats the motor at when your idling? Start from there.

 

when you put it in D does it lower the rpm below the point of your desired idle rpm? You oughta check out this article on diy-efi/gmecm by rbob on the iac..

i personally would remove as many steps as i could from everywhere on the chip having to do with the iac. If i recall correctly there is a table that adds steps starting at like 60 kpa and i think i had good success removing steps from that keeping the iac from going nuts. In retrospect id try and keep the iac from doing anything at all short of just helping the car start

 

It always wants to idle at 1100 rpm X 50 kPa. The problem is when you put it in gear is surges anywhere from 300 rpm to 2000 rpm and the kPa is all over the place.

yes. The commanded idle is 800 rpm and it wants to go to 600 sometimes and 300-2000 other times. Then the IAC slowly starts climbing and stays pegged