Minimum Air Idle Adjustment

[Roadster]

Just removed the TB, on my way to get the 7mm hex bolt...making progress....

Sent from my SM-G935P using ZR-1 Net Registry mobile app

[BlackZR1]

I know this is an old thread but just went through this procedure and it worked great for me so wanted to give a shout out to Dom and Phil for the procedure and tips. Thanks!
The only exception I ran into is that the 25mm long Hex head idle stop screw was a bit long in my case and the head was barely clearing one of the TB brackets when the throttles are almost full open so I used a 20mm long screw.
When I started, my IAC counts were 30 at idle. Now they are 10-12.
Thanks again.

[XfireZ51]

Originally Posted by BlackZR1

I know this is an old thread but just went through this procedure and it worked great for me so wanted to give a shout out to Dom and Phil for the procedure and tips. Thanks!
The only exception I ran into is that the 25mm long Hex head idle stop screw was a bit long in my case and the head was barely clearing one of the TB brackets when the throttles are almost full open so I used a 20mm long screw.
When I started, my IAC counts were 30 at idle. Now they are 10-12.
Thanks again.

Thanks Roger. Do you note any difference in idle or driving around?

[BlackZR1]

Originally Posted by XfireZ51

Thanks Roger. Do you note any difference in idle or driving around?

A couple weeks ago the car died a couple of times when coming to a stop which never happened before. I cleaned the IAC pintle and seat. Checked IAC counts at idle - was 30 which is high. Good news, high counts suggests no vacuum leaks but high counts at 650 rpm means the primary throttle blade opening at idle could be a tad too small which could explain stall when coming to a stop.
After finishing the idle setup yesterday, went for a drive today and drove perfectly - idle did not drop too low when taking my foot off the pedal and never died after an hour of driving and probably 2 dozen stops.
One more thing I will mention is that my original throttle stop screw measured 7.6mm extension from the mounting tab. I installed the new Hex head screw about 8mm extension (because I wanted more air through primary blade/less IAC counts) and this put me within a half-turn of my final adjustment.

[scorp508]

Digging up an old thread as I work through some stalling issues when coming to a stop before I go grab a data log. I realize this may be a "it depends" question, but is there a rough number of IAC steps one should expect to see with foot off the throttle at idle? I see BlackZR1 went from ~30 to 10-12 after following the procedure.

Thank you.

[XfireZ51]

Originally Posted by Roadster

Will get the 7mm hex head bolt later in the AM.
So the best way to do this is leave the throttle cable assembly attached to the TB, and remove as one unit, and just work on the TB in the engine compartment.

Another member also suggested the same.....thx....

U want enough IAC steps so ECM has room to ?catch? idle drop, but not too many steps to where most of idle air is coming thru IAC opening. I typically shoot for 10-15 steps. One other step I do is to modify the IAC Min Air table in the calibration to match what the actual IAC counts are in operation.

[scorp508]

Originally Posted by XfireZ51

U want enough IAC steps so ECM has room to ?catch? idle drop, but not too many steps to where most of idle air is coming thru IAC opening. I typically shoot for 10-15 steps. One other step I do is to modify the IAC Min Air table in the calibration to match what the actual IAC counts are in operation.

On a cold start when the desired idle is still 1250 it looks like IAC is at 110.

Once warm and desired idle of 850 the steps are around 30-40.

[scorp508]

Originally Posted by XfireZ51

One other step I do is to modify the IAC Min Air table in the calibration to match what the actual IAC counts are in operation.

It would appear I don't have this table as the only IAC related thing in my XDF is "IAC Position vs. Coolant Temp". My understanding (possibly wrong) is the IAC vs. CTS is only used during Open Loop. However, open loop does seem to be where most though not all of my stall issues take place.

Looks like it is in my best interests to go through the IAC procedure anyway and see where I land.

Currently it is mostly the same as the stock BMCB with a couple changes.

Deg C / Deg F / Steps
-40   / -40   / 95
-16   /   3   / 78 (Stock BCMB value is 90)
  8   /  46   / 51 (Stock BCMB value is 32)
 32   /  90   / 24 (Stock BCMB value is 12)
 56   / 133   / 10
 80   / 176   / 10
104   / 219   / 13
128   / 262   / 25
152   / 306   / 45

Is this table read as a base value, or in other words, "no less than this many steps" when the table is being utilized?