IAC doesn't seem to know what position it is in

[ryan_axberg]

I just my engine fired up for the first time and I am having issues with the IAC motor not being consistent at all. It is like it doesn't know what position it is at. I have done multiple IAC resets, where I unplug the sensor turn key on for 5 seconds, turn key off, plug it back in. It can work fine for the first fire, then if I turn it off and start it back up again it shows it has the same iac steps but it won't give the engine enough air to run, so I can tell it is actually closed not letting any air by it. I have also changed the iac reset position from 0 to 160 to 310 and it still isn't consistent at all. i have also swapped in a different iac motor and it does the same thing. I haven't ever come across this before and can't figure out what would be causing it. Does anyone have any idea?

[blindsquirrel]

Two things you can try:

If the IAC valve is disconnected and reconnected with the engine running, the idle speed may be wrong. If this occurs, reset the IAC valve by depressing the accelerator pedal slightly, start and run the engine for five seconds, then turn the ignition OFF for ten seconds.

Idle Learn Procedure

Anytime the powertrain control module (PCM) or the battery is disconnected, the PCM loses power, or the PCM is reprogrammed, the PCMs learned idle position is lost. The engine idle is unstable when the learned idle position is lost.

Perform the following procedure in order to return the learned idle to the correct position:

Automatic Transmission
1 Turn OFF the ignition.
2 Restore the PCM battery feed.
3 Turn OFF the A/C controls.
4 Set the parking brake and block the drive wheels.
5 Start the engine.
6 Ensure that the engine coolant temperature is more than 80?C (176?F).
7 Shift the transmission into Drive.
8 Allow the engine to idle for 5 minutes.
9 Shift the transmission into Park.
10 Allow the engine to idle for 5 minutes.
11 Turn OFF the engine for 30 seconds.

Manual Transmission
1 Turn OFF the ignition.
2 Restore the PCM battery feed.
3 Turn OFF the A/C controls.
4 Set the parking brake and block the drive wheels.
5 Place the transmission in Neutral.
6 Start the engine.
7 Ensure that the engine coolant temperature is more than 80?C (176?F).
8 Allow the engine to idle for 5 minutes.
9 Turn OFF the engine for 30 seconds.

[ryan_axberg]

I tried the reseting procedure you suggested and it didn't seem to change anything. I am using the same ecu that I had on a different engine that I had running good and I even flashed the same tune that from the other setup and it does the same thing. It fired up fine the first time with the iac position at like 110 at idle. I shut the engine off and tried to restart it right away. It barely started because of so little airflow and when adaptive idle came in it showed that the iac position was maxed out at 310 to maintain the same idle rpm as it was just before I shut the engine off, even though im sure it was in the same position that it was at idle 30 seconds prior. I got a cheap wiring harness off of ebay, not sure if this could be the problem or not.

[curiousg7]

What TB is it? Do you have a log with dynamic and desired airflow?

[ryan_axberg]

it is a stock truck drive by cable throttle body. I am logging idle desired airflow. I have tuned probably 7 or so vehicles that are drive by cable now and haven't ever come across this.

[ryan_axberg]

I just swapped in a different ecu that I had laying around that had a stock 5.3 calibration in it and it is still doing the same thing. Could it maybe be something weird in the wiring making it do that? I also swapped in a 3rd different iac motor that I know works just fine to rule that out and it still does the same thing.

[blindsquirrel]

screenshot.03-07-2021 18.27.14.png

[kevin87turbot]

When you get a chance, just attach a datalog, so we can see what's up. Make sure you include IAC position and TPS voltage as well.

[ryan_axberg]

It seemed like it was starting to be consistent now not so much. I logged it in park and my stit showed I needed to remove 47 lb/hr at 176 degrees coolant temp so I removed like 45 and flashed it back and that was the only change I made. And next log it showed I needed to add 60 lb/hr. Also my iac position in the first log at 176 degrees in park is 130 and in the second log it shows it is at like 200 for the same conditions in park. I didn't mess with the iac steps vs effective area, so my iac position should be at the same iac position at the same engine temp no matter what the stit are doing, or at least real close. Also to note no electric fans were on either time also no ac. And thanks blindsquirrel, I checked the wiring and it all looks correct. Also my stft were working when it was cold and after it warmed up a little they stopped, not sure what is going on with that either.

[ryan_axberg]

Here is another one of it. I just removed some braf and the IAC position gets all wacked. Might have to burn this thing soon. Same conditions same rpm and it shows that the IAC is way more open than it was just a minute before. I can't think of anything else to do on this piece of junk.

[jborders10]

Here is another one of it. I just removed some braf and the IAC position gets all wacked. Might have to burn this thing soon. Same conditions same rpm and it shows that the IAC is way more open than it was just a minute before. I can't think of anything else to do on this piece of junk.

Did you ever get this figured out ? I?m having the exact same issue .