IAC adjustment

skwatt

Member
I have a reading of 72-75 on the IAC setting on my scanmaster. The engine is at operating temp. I have tried adjusting the IAC with the screw on the driver's side of the TB. All it seems to do is adjust the idle. I have gone both ways and the IAC readings don't change. Am I adjusting the correct screw, or is there another? Could my IAC controller be bad and that is why it is not changing? I am desperate and this is the only reading that is out of whack.:confused:
 
I believe it's the screw under the gray rubber cap. You have to give the car a chance to settle after adjusting, it won't change immediately. If it never ever changes, then maybe it is not functioning.
 
From SW site.

With car in Park, engine fully warm, A/C off, look at the IAC counts on the scantool. If you wish to lower the count number, turn the adjustment screw clockwise. To increase the counts, turn it counterclockwise. Turn the screw a small increment, turn the engine off, and restart. This insures that the IAC resets and confirms the adjusted number. Continue until the desired number is achieved. Often, on stock set ups, about 1-1 1/2 threads of the adjustment screw will emerge thru on the lever side of the throttle body. Restarting also rezeros the tps as stated in the prior section and removes any effect on idle speed that may have occurred due to tps movement. The IAC counts will probably be 30 counts, or more, higher on a cold engine than on a warmed up engine. The counts will also be much higher in gear as compared to Park, and, higher with the AC turned on.

Remember that the IAC adjustment will change the TPS and that if the TPS moves past 0.46 volts, the idle may increase in speed as the ecm no longer thinks the car is in idle range. Therefore, if you are going to decrease IAC counts very much, it is a good idea to first lower the TPS down to 0.38 volts or so in order to prevent it from rising out of the idle range as you adjust the IAC.

It is not a bad idea to clean the throttle body out periodically with carb cleaner to keep the passages clean and to insure that the IAC function works correctly. Remove the IAC from the housing and clean any carbon or gum off the tip of the plunger and clean the seat as well. Don't power up the IAC when the unit is not installed. Otherwise, you may find the plunger is pushed out of the sensor. When reinstalling, very little torque is required. Just tighten enough to compress the gasket to prevent an air leak. Over tightening may crack the plastic interior of the IAC.
 
From SW site.

With car in Park, engine fully warm, A/C off, look at the IAC counts on the scantool. If you wish to lower the count number, turn the adjustment screw clockwise. To increase the counts, turn it counterclockwise. Turn the screw a small increment, turn the engine off, and restart. This insures that the IAC resets and confirms the adjusted number. Continue until the desired number is achieved. Often, on stock set ups, about 1-1 1/2 threads of the adjustment screw will emerge thru on the lever side of the throttle body. Restarting also rezeros the tps as stated in the prior section and removes any effect on idle speed that may have occurred due to tps movement. The IAC counts will probably be 30 counts, or more, higher on a cold engine than on a warmed up engine. The counts will also be much higher in gear as compared to Park, and, higher with the AC turned on.

Remember that the IAC adjustment will change the TPS and that if the TPS moves past 0.46 volts, the idle may increase in speed as the ecm no longer thinks the car is in idle range. Therefore, if you are going to decrease IAC counts very much, it is a good idea to first lower the TPS down to 0.38 volts or so in order to prevent it from rising out of the idle range as you adjust the IAC.

It is not a bad idea to clean the throttle body out periodically with carb cleaner to keep the passages clean and to insure that the IAC function works correctly. Remove the IAC from the housing and clean any carbon or gum off the tip of the plunger and clean the seat as well. Don't power up the IAC when the unit is not installed. Otherwise, you may find the plunger is pushed out of the sensor. When reinstalling, very little torque is required. Just tighten enough to compress the gasket to prevent an air leak. Over tightening may crack the plastic interior of the IAC.
Where the heck is that adjustment screw for the I.A.C. #'s???!!! The only adjustment I can find on my 86 G.N. is the idle set screw on the throttle linkage, I'm going nuts trying to find it.
 
Where the heck is that adjustment screw for the I.A.C. #'s???!!! The only adjustment I can find on my 86 G.N. is the idle set screw on the throttle linkage, I'm going nuts trying to find it.
The adjustment screw he is talking about is the throttle stop screw. It's technically not an idle adjustment screw. Its a throttle stop screw. The computer controls the idle with the IAC.
 
Okay your IAC is high so you are going to screw that screw
In Alil to open the throttle blade . After you do that then go to your tps and Lower it back down to .42 . Opening the throttle blade will lower your IAC closing the blade will raise the IAC count . There is no direct adjustment screw to the IAC .
 
The adjustment screw he is talking about is the throttle stop screw. It's technically not an idle adjustment screw. Its a throttle stop screw. The computer controls the idle with the IAC.
I KNEW IT!!!
A buddy of mine that is a old school "Mopar" head said the same thing to me. He said, I believe that Buick G.N. I.A. control is controlled by the on board E.C.M. by the foot of the passenger side, inside the car.
But Mike, If you research this Turbo Buick site, everyone is saying the idle air adjustment screw is on the drivers side of the throttle body with a gray cap over it on the linkage side. They even go so far as to say that many people confuse this with the idle set screw. BUT IT IS THE IDLE SET SCREW!!!! I was pul;ing my hair out. I knew that was an idle set screw and NOT anything to do with adjusting the I.A.C. motor !!!!
Thank's for clearing this up for me.
I decided to take the car next week to a specialty shop near me. If you google, "The Lost Art of EFI Service" You can see the write up the place received in 2007 in Hemming's magazine.
I'm at the point of just saying, Hey, I'm an Operating Engineer for H.V.A.C. Why the hell did I ever decide to start touching this is beyond me.
Each man to his own trade.
I don't mind doing an oil change or rad flush, But I have no business adjusting technical settings.
AlthougnhI would have liked to if I had good direction.
 
That's the screw, it's the IAC adjustment screw.
If That's the screw, Which I believe it is now. Then why is it that so many people are saying that this screw is often confused as being the idle set screw.
From what I understand, The I.A.C. adjustment is controlled by the E.C.M. only.
 
From SW site.

With car in Park, engine fully warm, A/C off, look at the IAC counts on the scantool. If you wish to lower the count number, turn the adjustment screw clockwise. To increase the counts, turn it counterclockwise. Turn the screw a small increment, turn the engine off, and restart. This insures that the IAC resets and confirms the adjusted number. Continue until the desired number is achieved. Often, on stock set ups, about 1-1 1/2 threads of the adjustment screw will emerge thru on the lever side of the throttle body. Restarting also rezeros the tps as stated in the prior section and removes any effect on idle speed that may have occurred due to tps movement. The IAC counts will probably be 30 counts, or more, higher on a cold engine than on a warmed up engine. The counts will also be much higher in gear as compared to Park, and, higher with the AC turned on.

Remember that the IAC adjustment will change the TPS and that if the TPS moves past 0.46 volts, the idle may increase in speed as the ecm no longer thinks the car is in idle range. Therefore, if you are going to decrease IAC counts very much, it is a good idea to first lower the TPS down to 0.38 volts or so in order to prevent it from rising out of the idle range as you adjust the IAC.

It is not a bad idea to clean the throttle body out periodically with carb cleaner to keep the passages clean and to insure that the IAC function works correctly. Remove the IAC from the housing and clean any carbon or gum off the tip of the plunger and clean the seat as well. Don't power up the IAC when the unit is not installed. Otherwise, you may find the plunger is pushed out of the sensor. When reinstalling, very little torque is required. Just tighten enough to compress the gasket to prevent an air leak. Over tightening may crack the plastic interior of the IAC.
I Like this write up!!!
I'm going to take another crack at this.
I didn't allow the engine to be at operating temperature at my last adjustment, mainly due to the fact that the silicone hose for the turbo inlet was flush up against the i.a.c. connector and I couldn't unplug it to clean inside the housing ( Would have been too hot to touch everything).
I think I'll go back in the garage now, Allow it to get up to operating temp ( 165) and attempt adjustments again.
Seems as though since I did the adjustment the other day without allowing for warm engine has cause my car now to no longer properly boost up, or, when it does, it falls flat on it's face. Whereas before it was like a 747 on take off and your back was inprinted in the seat!
 
I thought I already went over this . To raise the IAC you close the throttle blade with that screw . To lower it you open the throttle blade . After that you have to rest the tps to .42 .
http://www.gnttype.org/techarea/faq/IACresetscan.html
I screwed up, although I followed this procedure, I failed to allow the engine to get up to operating temp.
I wanted to remove the I.A.C. completely to clean the housing as well as the throttle plate, etc..
After I cleaned it up, I performed the I.A.C. reset using a paper clip ( jumped A/B on ALDL) and followed the steps.
I then started the car and adjusted the RPM's via the throttle stop screw to 500rpm, shut the car OFF, turned the key to "ON" position and adjusted the TPS to .44
Correct me if I'm wrong, But I screwed up by NOT doing this procedure with the engine already being in what's called a "closed loop" already warmed up?
Thank's for your help
 
I screwed up, although I followed this procedure, I failed to allow the engine to get up to operating temp.
I wanted to remove the I.A.C. completely to clean the housing as well as the throttle plate, etc..
After I cleaned it up, I performed the I.A.C. reset using a paper clip ( jumped A/B on ALDL) and followed the steps.
I then started the car and adjusted the RPM's via the throttle stop screw to 500rpm, shut the car OFF, turned the key to "ON" position and adjusted the TPS to .44
Correct me if I'm wrong, But I screwed up by NOT doing this procedure with the engine already being in what's called a "closed loop" already warmed up?
Thank's for your help
Just make sure the car is warmed up . It will go into closed loop after car is runing for at least 30sec and it's above 130 degrees . Here is another way to reset the IAC http://www.gnttype.org/techarea/faq/IACreset.html
 
Another thing to note after you jump the ALDL terminal and the IAC numbers happen to drop down to zero you may very well have a bad IAC motor. I did this on a buddy's car recently and the IAC numbers were ok after reset but then were totally out of wack after start up. Then slowly dropped to zero. It's always recommended that you take the IAC motor out and clean off the tip so you get a good sealing surface when the plunger goes in.


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Just make sure the car is warmed up . It will go into closed loop after car is runing for at least 30sec and it's above 130 degrees . Here is another way to reset the IAC http://www.gnttype.org/techarea/faq/IACreset.html
Thank you.
I purchased a new I.A.C. motor because even though I remove it, cleaned it up, and also performed the reset, the car fortunately no longer drops dead after a highway run and certainly idles a lot better and steady, 800 810 rpm but the i.a.c. #" are still showing in the high 60's in park when idling.
From what I understand, it should be between 10/20 when in closed loop.
In addition to that, My intake on the turbo ( silicone hose adaptor) is right up against the connector of the i.a.c. making it a project just to unplug it as required for a reset.
I'll have to install an angle plate ( 45 deg's) for future ease in removal/cleaning.
 
Thank you.
I purchased a new I.A.C. motor because even though I remove it, cleaned it up, and also performed the reset, the car fortunately no longer drops dead after a highway run and certainly idles a lot better and steady, 800 810 rpm but the i.a.c. #" are still showing in the high 60's in park when idling.
From what I understand, it should be between 10/20 when in closed loop.
In addition to that, My intake on the turbo ( silicone hose adaptor) is right up against the connector of the i.a.c. making it a project just to unplug it as required for a reset.
I'll have to install an angle plate ( 45 deg's) for future ease in removal/cleaning.
You do not need to unplug the IAC connector. If you want your IAC number to move lower,turn the throttle set screw in clockwise 1/2 turn. Reset the idle TPS number to .40 ignition on,engine not running. With the engine running,you should see a TPS number of .42. If not,turn in some more when it is running.
 
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