IACV = Idle Air Control Valve and it has the pintle which is the end that extends and retracts to change the quantity of air that bypasses the throttle plate when you are in the idle position. So we know we have X amount of fuel injected at idle and we want the AFR to be correct or we may get a idle that wanders, hard to start or just shuts off if far enough out.
The IACV has a range that it operates in which is 0-255, 255 which is leaner AFR as the pintle is retracted all the way opening the port as far as it can and allowing max air to bypass the throttle blade when in a closed position.
Obvisouly 0 would be the opposite and extend as far as it can and close off the port bypassing the throttle plate thus making it richer.
You may hear the term stepper motor which is the little motor inside the IACV that extends or retracts the pintle based off signal from the ECM.
It is not real often you hear of one going bad but this is something to keep in mind and check for idle quality issues.
I am sure everyone has a method they have to resetting the IACV and not saying anyone is incorrect just showing a method using Hud Ecu Hacker,
You of course will need a windows based laptop with Hud Ecu Hacker installed as well as the cables to connect to the diagnostic port so you have control of the ecu in the data slewing mode.
Step 1: Is remove the IACV and lay it off to the side where the pintle will not be obstructed. Below is a pic of one on the unit I was working on today. I did not measure the actual pintle extension here as my only goal was to reset it to make sure it was correct.
Step 2: Is with Hud Ecu Hacker connected follow the video and it will show you what needs to be done in Hud Ecu Hacker.
Open the Data Slew window and set the IACV to absolute 255 position and click Send all presets to ECU
Step 3: Now you want to disconnect the battery WITHOUT turning off ignition as you need a instantaneous removal of power or the ECU will save the pintle position as the parked position and we don't want that.
Step 4: Reconnect the battery and perform Step 2 again if in doubt that the IACV pintle is fully retracted.
Verify that the pintle is fully retracted and if the spring is fully collapsed and you set 255 again you will hear a chirping sound as the stepper motor is trying to retract more but can't retract anymore.
Step 5: If everything looks good then it is time to reset all presets in the ecu following this video.
Now at this point if all went well and IF the IACV was out of whack you should be presented with a better idle quality.