Minimum Air Idle Adjustment

[XfireZ51]

There's been several threads whee this topic comes up. I had documented it as part of another thread but thought I would set it up for its own to make it easier to find. Would make a good sticky.

OK. Here goes:

As for setting the IAC count for Minimum Air, the procedure I follow is:
(Do this procedure once you have warmed motor to C/L operating temps. otherwise it may very well not idle. Also, you will have converted your throttle stop stud to a hex bolt I think a 7mm hex head.)

1. Jumper the ALDL as you would for reading codes.
2. Turn ignition to ON, not start.
3. Leaving ignition ON, remove the IAC harness connector. This fully extends the IAC pintle and closes off the IAC port.
4. Shut ignition OFF and remove the ALDL jumper.
5. Start the motor and get it to idle. May need to use a bit of throttle at first.
6. Check idle rpm. Turn the throttle stop screw until the motor is idling at an rpm just below what your target idle rpm. I want my idle at 875-900, so I set Min Air throttle at 800-825rpm. You may need to adjust TPS Voltage so that ECM stays within idle TPS Voltage range.
7.Tighten everything up and shutoff motor.
8. Plug in IAC. I also undo the negative BATT cable to drain the ECM memory.
9. Reconnect BATT turn ignition ON, and check TPS V. Adjust to .53-.57v if necessary.
10. Start motor and quickly raise to ~2000rpm for a brief period. This resets the IAC.
11. Shutoff motor, then restart. Allow motor to idle down and check your IAC counts and your TPS Volt which may need to be adjusted one more time.

[Dynomite]

There's been several threads whee this topic comes up. I had documented it as part of another thread but thought I would set it up for its own to make it easier to find. Would make a good sticky.

OK. Here goes:

As for setting the IAC count for Minimum Air, the procedure I follow is:
(Do this procedure once you have warmed motor to C/L operating temps. otherwise it may very well not idle. Also, you will have converted your throttle stop stud to a hex bolt I think a 7mm hex head.)

1. Jumper the ALDL as you would for reading codes.
2. Turn ignition to ON, not start.
3. Leaving ignition ON, remove the IAC harness connector. This fully extends the IAC pintle and closes off the IAC port.
4. Shut ignition OFF and remove the ALDL jumper.
5. Start the motor and get it to idle. May need to use a bit of throttle at first.
6. Check idle rpm. Turn the throttle stop screw until the motor is idling at an rpm just below what your target idle rpm. I want my idle at 875-900, so I set Min Air throttle at 800-825rpm. You may need to adjust TPS Voltage so that ECM stays within idle TPS Voltage range.
7.Tighten everything up and shutoff motor.
8. Plug in IAC. I also undo the negative BATT cable to drain the ECM memory.
9. Reconnect BATT turn ignition ON, and check TPS V. Adjust to .53-.57v if necessary.
10. Start motor and quickly raise to ~2000rpm for a brief period. This resets the IAC.
11. Shutoff motor, then restart. Allow motor to idle down and check your IAC counts and your TPS Volt which may need to be adjusted one more time.

Dominic ........Great Information and by the NUMBERS :thumbsup::thumbsup:
In -Solutions- Page #4 under THROTTLE BODY AND AIR INTAKE
Air Idle Adjustment TIPS (http://www.zr1.net/forum/showthread.php?t=27764)

[Roadster]

Thanks very much for posting the procedure. Tried looking up the info as you mentioned, but no luck. So this comes in very handy....:handshak::cheers:

I also am assuming that the "nut" is permanently attached to the bracket and only the stud gets removed in order to thread in the 7mm hex head bolt, correct???

[Jagdpanzer]

Tom,
The nut is not attached.
Getting the old Allen set screw out can be a real pain.
Spare the drama and remove the TB and do it on the bench. If the set screw fights backing out go the other way and screw it all the way through the other direction. Be sure to hit it with some penetrating oil.

[Roadster]

Appreciate the reply Phil, sounds like the way to go....I might just try one more thing before removing the TB....thanks...

[Roadster]

Tom,
The nut is not attached.
Getting the old Allen set screw out can be a real pain.
Spare the drama and remove the TB and do it on the bench. If the set screw fights backing out go the other way and screw it all the way through the other direction. Be sure to hit it with some penetrating oil.

Phil,
Taking your advice and going to remove the TB within a few days. Hopefully I'll get it all right and idling just fine!!! :)

[XfireZ51]

Here's a pic of my throttle stop.

[Roadster]

Thank you sir, have seen that on mine and as said a real PIA to get to with everything attached.
Some simple questions....

1- other than removing the IAC, TPS connectors and various hoses, can the throttle cable assembly come off with the one Torx 25 screw that is above the throttle stop screw and along with the 2 cable screws attached to the plenum?
2- and since everything is still together, will the cable need to be re adjusted when assembled?

Been looking through the FSM, but couldn't find what I was looking for!!!

thanks for any info......

[XfireZ51]

Except that mine shows the 7mm hex head installed.
You need to unplug IAC harness connector and TPS connector but should be able to able to work w TB without disconnecting cable throttle cable. Obviously the airhorn comes off also along w undoing the throttle cable retainers on the plenum.

[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....

[Roadster]

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

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[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]

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]

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]

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]

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]

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?

[scorp508]

One small note for any future people. I was having trouble with this procedure as I didn't use the correct ALDL pin combo on my 94 to extend the pintle. I needed to use pins 4 & 6 to use the Service Engine Soon light to flash. Only this combo fully extended the IAC pintle on my 94. The other ALDL pin combos for CCM on the digital dash or the flashing Service Ride Control light do not work to extend it.

[tpepmeie]

One small note for any future people. I was having trouble with this procedure as I didn't use the correct ALDL pin combo on my 94 to extend the pintle. I needed to use pins 4 & 6 to use the Service Engine Soon light to flash. Only this combo fully extended the IAC pintle on my 94. The other ALDL pin combos for CCM on the digital dash or the flashing Service Ride Control light do not work to extend it.



I feel like I knew this at one time, but was this a model year change, regarding the ALDL pin combination for the IaC? If so, when did it change?



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[tpepmeie]

Oh, nvm. I saw in the other post where you had been reading the ccm and ride control modules instead of the ECM codes. I recall the 95 has kind of a hybrid ALDL connector. OBD2 style, but the ECM is obviously OBD1 for the LT5.


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[XfireZ51]

Todd,

94 is when GM went to 16pin ALDL which would be used for OBDII cars. LT5 got it altho still OBD1

[XfireZ51]

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.

So looks like u should open TB a bit further which then would require fewer IAC steps for idle.
Again, make sure u re-check TPS v whenever u change TB opening.

[scorp508]

So looks like u should open TB a bit further which then would require fewer IAC steps for idle.
Again, make sure u re-check TPS v whenever u change TB opening.

That was before getting my adjustment done properly yesterday. Now It's low-mid 20s once warm at a 850 idle, but I'll try to get it a little lower when I have some time. :cheers: I'm nearly out of thread on the stop screw, so there's not much more to give unless I get a longer screw.