Idle Air Control Solenoid Question?

[1-ton]

I have a brand new GM crate engine, which has all new sensors. One of the new sensors is the IAC solenoid. The question I have is about the initial start up of the engine. How do I get the IAC solenoid to adjust itself "in the ballpark" for the initial start up? I have read some things about the IAC self adjusting itself just by turning the ignition to the Start position a couple of times. Would this be correct? Since this is an older GM engine with a flat tappet cam, I have to fire this thing up, and run the RPM's up to 2000 RPM immediately and leave it there for 20 minute s at least. After that if the idle is not correct, I will do a total adjustment of the IAC, which includes setting the idle screw on my TBI unit with the IAC disconnected. Thanks for any suggestions on this.

 

[dyeager535]

What I found in a quick search, from thirdgen.org is:

"2. IAC reset/min idle speed- This sets the throttle plate on the throttle body to a specific rpm. I recommend about 500 rpm for most engines. Procedures- Go to sheet 7 of the pinout diagrams. At the top is the ALDL connector. You need to put a jumper between pins A and B of the connector. These are pins A9(wht/blk) and A12 (blk/wht) on the ECM. This puts the ECM into aldl mode. Turn the key on (not start) and the IAC should drive completely closed. You will normally hear a buzzing from the IAC. If you have the winaldl up and running on your laptop, you should see the IAC went from 145 to 0. Now unplug the IAC connector. turn the key off. Remove jumper. Start motor. If the idle is too low you may have to keep it running. On the front drivers side of the throttle body is the adjustment screw. It may be behind a silver plug. If so just use a nail or punch to poke it and remove it. Then use a #20 torx bit to adjust the idle speed to at least 100 rpm less then your warm idle speed. if 600 then set to 500 rpm. You are looking for the lowest consistant idle your motor will do. When set, turn off motor and reconnect the IAC. I try to keep the IAC count to at least 40 with the motor warm and idling."

Obviously idle RPM isn't going to matter as you break the cam in, but once done you may have to mess with the screw. Or not, you'll know once it's broken in and tries to idle.

One of the reasons I hate starting with EVERYTHING new. If something goes wrong, harder to nail down what isn't right, since new doesn't equal good anymore.

 

[1-ton]

Thanks for the reply. I guess when I bring the RPM's up to break in the cam, it will not matter what the IAC is doing because it has no effect on anything above idle anyway. Thank s for the procedure post because I may be referring back to this post at a later date if the idle is not correct after the cam break in procedure.

" One of the reasons I hate starting with EVERYTHING new. If something goes wrong, harder to nail down what isn't right, since new doesn't equal good anymore. "

I did buy as many AC/DELCO and Delphi OEM sensors as is available any more. The IAC is a Delphi unit I got from RockAuto. My truck also had all of the original GM sensors it came with from the factory. Many of them where dry rotted, cracked, and rusted from old age. Any of those that seemed to be OK I cleaned the dirt and grease off of them and kept for use on my new crate engine.

 

[dyeager535]

How many of those Delco/Delphi boxes have "china" on them now?

Sometimes you get lucky and get the bit older stuff that is Mexico or even US, but sounds like most everything new is coming from china now.

That is the unfortunate thing with the engine sensors. I don't think GM used a very high quality plastic on many of them, or the designs weren't real sturdy (TBI TPS and the O2 sensor connector come to mind) so you do end up with broken connectors or components that need replaced. Not sure I can blame GM on stuff that is ~30+ years old, but I will anyway.

I'll be going through the new engine break in as well, hopefully sooner rather than later, but most of my components are ~10 years old, so they should make the transition without too much problem. I hope.