what counts is the iac supposed to start and idle at?
02-06-2013, 07:01 PM
#1
Registered User
Thread Starter
Join Date: May 2012
Location: idaho
Posts: 660
what counts is the iac supposed to start and idle at?
Ive been questioning my iac valve. It doesnt operate consistant(via datalogging). Ive had it between 130 and 4 counts at idle. Most of the time on cold start its 130ish and eventually drops to 90. I also have times it dont want to drop and will high idle(2000rpm) I have times when the count and the memory count is so far off it will stall at a stop without feathering gas. There are also times it wont increase in counts with higher revs. I have had it out and cleaned the pintle(whole thing very dirty). I dont want to buy another if I dont have too but sure seams like I may have too. Is there anything you can clean and or lube it with so it wont stick? I have read Freds pcm tutorial and mine has only dropped to single digits one time in all of my monitering(probably ly 15 times and 3hours worth). Any input would be appreciated. I assume if I do need to replace it is the ac delco the desirable choice? Was quoted like $160 for it and thats with the guy at dealership giving a price cut. Thanks
02-06-2013, 11:10 PM
#2
Administrator
Join Date: Nov 1998
Location: Hell was full so they sent me to NJ
Posts: 70,825
Re: what counts is the iac supposed to start and idle at?
When it's idling at 2,000 rpm, what does the PCM do with the IAC counts to try adjust the rpm? They should drop. If counts drop and RPM doesn't, then the IAC motor isn't responding. Have you checked the resistance of the coils? How did you clean the pintle? Did you attempt to move it? Have you tried cleaning the IAC plate passages?
Given the engine you list in your signature, you've had the PCM tuned. One of the tables is idle speed vs. coolant temp. That provides an increased idle speed on very cold starts. Stock programming has a max RPM of 1,200 at sub-zero coolant temps. Do you have any idea if the programmer adjusted that table? What is the idle set at in the program for full operating temp?
Based on your other active thread it appears you are having trouble with idle air flow through an unidentified brand of throttle body. You indicate the air was not even directed to the IAC, and the passage was also blocked by your nitrous plate, in which case it would render the IAC control useless, and then that you opened up a passage, or something. It's sort of hard to answer this question in light of the issues you've posted in the other thread.
Given the engine you list in your signature, you've had the PCM tuned. One of the tables is idle speed vs. coolant temp. That provides an increased idle speed on very cold starts. Stock programming has a max RPM of 1,200 at sub-zero coolant temps. Do you have any idea if the programmer adjusted that table? What is the idle set at in the program for full operating temp?
Based on your other active thread it appears you are having trouble with idle air flow through an unidentified brand of throttle body. You indicate the air was not even directed to the IAC, and the passage was also blocked by your nitrous plate, in which case it would render the IAC control useless, and then that you opened up a passage, or something. It's sort of hard to answer this question in light of the issues you've posted in the other thread.
02-07-2013, 03:19 AM
#3
Registered User
Thread Starter
Join Date: May 2012
Location: idaho
Posts: 660
Re: what counts is the iac supposed to start and idle at?
When it's idling at 2,000 rpm, what does the PCM do with the IAC counts to try adjust the rpm? They should drop. If counts drop and RPM doesn't, then the IAC motor isn't responding. Have you checked the resistance of the coils? How did you clean the pintle? Did you attempt to move it? Have you tried cleaning the IAC plate passages?
.................................................. .................................................
Im sorry I forgot to include a few helpful details. When starting cold(after driven 15 miles to get home and sits overnight) it fires up and idles 1200rpm ish and then drops. The counts dont seem to move at all until after warm and have a few miles on it(no movement reguardless of rpm and at 130 counts which is what it is at before startup). Then what it does most of the time is 12 miles from there(all highway) I hit a stoplight and that is when it wants to idle around 2000rpm. If i stab the throttle it will usually kick down(like a sticky choke).
The counts once they begin to move are very sluggish and eventually start to move what i assume to be closer to normal(will rapidly climb with rpm). When its like this idle behaves well(moving rapidly with rpm changes). From what I recall when 2000rpm idle the counts stay at the same spot as does the rpm(will watch closer to confirm this) until I stab the throttle then most of the time it will drop but only 7 counts or so but the rpm will drop.
I have not checked the coils(havent read or seen anything about that in my searches) please explain or direct me.
I cleaned the pintle with throttle body cleaner and paper towel.
I did not try to move it.
The throttle body was new and the manifold was cleaned so all that should have been fine.
Car sat for over two and a half years before putting this iac into new tb.
__________________________________________________ _____________
Given the engine you list in your signature, you've had the PCM tuned. One of the tables is idle speed vs. coolant temp. That provides an increased idle speed on very cold starts. Stock programming has a max RPM of 1,200 at sub-zero coolant temps. Do you have any idea if the programmer adjusted that table? What is the idle set at in the program for full operating temp?
.................................................. ..................................................
Yes pcm is tuned and not sure if any adjustments were made there but the way it starts and idles in the morning is normal(or close)
__________________________________________________ _____________
Based on your other active thread it appears you are having trouble with idle air flow through an unidentified brand of throttle body. You indicate the air was not even directed to the IAC, and the passage was also blocked by your nitrous plate, in which case it would render the IAC control useless, and then that you opened up a passage, or something. It's sort of hard to answer this question in light of the issues you've posted in the other thread.
.................................................. .................................................
Im sorry I forgot to include a few helpful details. When starting cold(after driven 15 miles to get home and sits overnight) it fires up and idles 1200rpm ish and then drops. The counts dont seem to move at all until after warm and have a few miles on it(no movement reguardless of rpm and at 130 counts which is what it is at before startup). Then what it does most of the time is 12 miles from there(all highway) I hit a stoplight and that is when it wants to idle around 2000rpm. If i stab the throttle it will usually kick down(like a sticky choke).
The counts once they begin to move are very sluggish and eventually start to move what i assume to be closer to normal(will rapidly climb with rpm). When its like this idle behaves well(moving rapidly with rpm changes). From what I recall when 2000rpm idle the counts stay at the same spot as does the rpm(will watch closer to confirm this) until I stab the throttle then most of the time it will drop but only 7 counts or so but the rpm will drop.
I have not checked the coils(havent read or seen anything about that in my searches) please explain or direct me.
I cleaned the pintle with throttle body cleaner and paper towel.
I did not try to move it.
The throttle body was new and the manifold was cleaned so all that should have been fine.
Car sat for over two and a half years before putting this iac into new tb.
__________________________________________________ _____________
Given the engine you list in your signature, you've had the PCM tuned. One of the tables is idle speed vs. coolant temp. That provides an increased idle speed on very cold starts. Stock programming has a max RPM of 1,200 at sub-zero coolant temps. Do you have any idea if the programmer adjusted that table? What is the idle set at in the program for full operating temp?
.................................................. ..................................................
Yes pcm is tuned and not sure if any adjustments were made there but the way it starts and idles in the morning is normal(or close)
__________________________________________________ _____________
Based on your other active thread it appears you are having trouble with idle air flow through an unidentified brand of throttle body. You indicate the air was not even directed to the IAC, and the passage was also blocked by your nitrous plate, in which case it would render the IAC control useless, and then that you opened up a passage, or something. It's sort of hard to answer this question in light of the issues you've posted in the other thread.
Throttle body is 58mm tpis. Yes the tpis tb is like the other 58mm tb ive seen and just dumps the iac air behind the butterflys and they had the blades slightly open. The nitrous plate had a 1/4" hole that would let some air in the iac passage but because of the design of the aftermarket tb actually restriced it(would work with stock tb). I closed the blades and reset the tps. Then I plugged the opening that would dump the iac air behind the butterflys by using a brass tube(rifle casing). That forces the iac air to go into the iac passage. I opened the hole through the nitrous plate to 1/2" and the brass tube feeds through it. Then i drilled from the front of throttle body straight through into were the 1/2 tube is. This mimmicks the stock throttle body so to speak and is what many people do to help split blms at idle and low rpm.
Last edited by slick1hunting; 02-07-2013 at 03:29 AM. Reason: Make easier to read.
02-07-2013, 03:42 AM
#4
Registered User
Thread Starter
Join Date: May 2012
Location: idaho
Posts: 660
Re: what counts is the iac supposed to start and idle at?
I found this with a better formatted search. http://shbox.com/1/iac2.jpg
02-07-2013, 05:27 AM
#5
Administrator
Join Date: Nov 1998
Location: Hell was full so they sent me to NJ
Posts: 70,825
Re: what counts is the iac supposed to start and idle at?
And all the numbers you are mentioning... idle speed, IAC counts, etc..... were they observed BEFORE of AFTER you attempted to get the air to flow into the IAC passage?
What does this mean:
"When its like this idle behaves well(moving rapidly with rpm changes). "
Do you mean the IAC moves correctly to control the RPM?
Have you checked the throttle linkage to make sure its not binding when it gets hot?
What does this mean:
"When its like this idle behaves well(moving rapidly with rpm changes). "
Do you mean the IAC moves correctly to control the RPM?
Have you checked the throttle linkage to make sure its not binding when it gets hot?
02-07-2013, 01:36 PM
#6
Registered User
Thread Starter
Join Date: May 2012
Location: idaho
Posts: 660
Re: what counts is the iac supposed to start and idle at?
And all the numbers you are mentioning... idle speed, IAC counts, etc..... were they observed BEFORE of AFTER you attempted to get the air to flow into the IAC passage?
What does this mean:
"When its like this idle behaves well(moving rapidly with rpm changes). "
Do you mean the IAC moves correctly to control the RPM?
Have you checked the throttle linkage to make sure its not binding when it gets hot?
What does this mean:
"When its like this idle behaves well(moving rapidly with rpm changes). "
Do you mean the IAC moves correctly to control the RPM?
Have you checked the throttle linkage to make sure its not binding when it gets hot?
02-07-2013, 02:53 PM
#7
Registered User
Join Date: Dec 1969
Location: Little Rock, AR
Posts: 27,714
Re: what counts is the iac supposed to start and idle at?
This may not be your scenario, but it's normal for RPMs to stay up when you push in the clutch and before you come to a stop. You may notice that when you finally get stopped, that the idle does come down (even my automatic does this to an extent). Many people complain about this, but there is a function in the PCM called the "throttle follower" that does this. It is meant to keep the engine from stalling when the TB blades suddenly close.
02-07-2013, 04:34 PM
#8
Registered User
Thread Starter
Join Date: May 2012
Location: idaho
Posts: 660
Re: what counts is the iac supposed to start and idle at?
This may not be your scenario, but it's normal for RPMs to stay up when you push in the clutch and before you come to a stop. You may notice that when you finally get stopped, that the idle does come down (even my automatic does this to an extent). Many people complain about this, but there is a function in the PCM called the "throttle follower" that does this. It is meant to keep the engine from stalling when the TB blades suddenly close.
02-08-2013, 09:46 AM
#9
Administrator
Join Date: Nov 1998
Location: Hell was full so they sent me to NJ
Posts: 70,825
Re: what counts is the iac supposed to start and idle at?
. Ive also noticed the counts havent been very consistant. It really seems like it cant move much when first started and then as it moves it gains range of motion(but only if its kept moving). It is really affected by steady rpm not wanting to move much but with alot of varying rpm and throttle the counts are very responsive and it seems to work as intended.
I'm not sure how it could "work as intended" if the IAC passage was blocked as you indicated, before you opened it up. Something doesn't make sense if the PCM has been changing the IAC counts and the IAC has been controlling the idle, even with the passage blocked.
02-08-2013, 01:07 PM
#10
Registered User
Thread Starter
Join Date: May 2012
Location: idaho
Posts: 660
Re: what counts is the iac supposed to start and idle at?
You do understand that the "counts" are the position the PCM is telling the IAC valve to go to? It is not the actual position of the valve. There is no feedback from the valve to the PCM.
I'm not sure how it could "work as intended" if the IAC passage was blocked as you indicated, before you opened it up. Something doesn't make sense if the PCM has been changing the IAC counts and the IAC has been controlling the idle, even with the passage blocked.
I'm not sure how it could "work as intended" if the IAC passage was blocked as you indicated, before you opened it up. Something doesn't make sense if the PCM has been changing the IAC counts and the IAC has been controlling the idle, even with the passage blocked.
02-08-2013, 01:08 PM
#11
Registered User
Thread Starter
Join Date: May 2012
Location: idaho
Posts: 660
Re: what counts is the iac supposed to start and idle at?
This is from your tutorial and my counts are vastly different looking............... IAC (Idle Air Control):
The Idle Air Control is a little stepper motor that moves a pintle in and out of a hole in the throttle body,and allows air to bypass the throttle blades,and enter the intake manifold. This is required to allow the car to idle when the throttle blades are completely closed (as they should be). The PCM plays with the IAC motor to keep the idle at spec,800rpm for M6's and 650rpm for A4's. The ScanMaster reads the "position" of the valve motor,which can range from "1" to "255". At idle, you should see roughly "20" to "40" (this is fomr my M6,idling at 800rpm). And,it should be steady. Any lower and you probably have a vacuum leak,or the throttle return stop screw on the throttle body is preventing the blades from fully closing. If you see numbers higher than this at idle,it is possible you have a dirty IAC motor pintle which is not moving correctly,or plugged air passages leading to the IAC motor. If you have installed a throttle boy airfoil,it is possible it is blocking air flow through the opening that supplies air to the IAC system.
When you start to drive,the IAC value will start to rise. This is done in order to keep enough air flowing into the manifold that if you suddenly let off on the throttle,and let the blades fully closed,there will be enough air to keep the motor from stalling,and provides air to minimize pollutants. The counts I have seen under cruising and WOT conditions are in the range of 60 - 100.
The IAC motor is located at the base of the throttle body,on the passenger side. The PCM stores the "learned" idle position,so that it can return to this value quickly,in order to control idle. This stored value can be "lost" if the power to the PCM is lost,and idle may hunt a bit on startup until the value is relearned.
The Idle Air Control is a little stepper motor that moves a pintle in and out of a hole in the throttle body,and allows air to bypass the throttle blades,and enter the intake manifold. This is required to allow the car to idle when the throttle blades are completely closed (as they should be). The PCM plays with the IAC motor to keep the idle at spec,800rpm for M6's and 650rpm for A4's. The ScanMaster reads the "position" of the valve motor,which can range from "1" to "255". At idle, you should see roughly "20" to "40" (this is fomr my M6,idling at 800rpm). And,it should be steady. Any lower and you probably have a vacuum leak,or the throttle return stop screw on the throttle body is preventing the blades from fully closing. If you see numbers higher than this at idle,it is possible you have a dirty IAC motor pintle which is not moving correctly,or plugged air passages leading to the IAC motor. If you have installed a throttle boy airfoil,it is possible it is blocking air flow through the opening that supplies air to the IAC system.
When you start to drive,the IAC value will start to rise. This is done in order to keep enough air flowing into the manifold that if you suddenly let off on the throttle,and let the blades fully closed,there will be enough air to keep the motor from stalling,and provides air to minimize pollutants. The counts I have seen under cruising and WOT conditions are in the range of 60 - 100.
The IAC motor is located at the base of the throttle body,on the passenger side. The PCM stores the "learned" idle position,so that it can return to this value quickly,in order to control idle. This stored value can be "lost" if the power to the PCM is lost,and idle may hunt a bit on startup until the value is relearned.
02-08-2013, 01:24 PM
#12
Registered User
Thread Starter
Join Date: May 2012
Location: idaho
Posts: 660
Re: what counts is the iac supposed to start and idle at?
This link shows the way the 58mm dump the air behind the butterfies rather than in the passage in the intake like the stock tb. I didnt fill the gap with a spacer I used brass tubing to do the same function. http://m.ls1tech.com/forums/showthre...325&styleid=25
Last edited by slick1hunting; 02-08-2013 at 01:25 PM. Reason: forgot to add link
02-08-2013, 02:14 PM
#13
Administrator
Join Date: Nov 1998
Location: Hell was full so they sent me to NJ
Posts: 70,825
Re: what counts is the iac supposed to start and idle at?
It might not move if the pintle is stuck or damaged. You indicate you cleaned it off with a paper towel. A soft brush would have been a better choice. The factory manual cautions that moving the pintle on a used IAC valve can damage it.
The pintle could be moving, but the passages may be plugged.
You seem to be suggesting the problem is my writeup. That was made specifically for a STOCK engine. Once you start changing things - stroker, cam, PCM reprogram, redirecting air to other places, aftermarket throttle body - you can't hold me responsible for what I wrote not reflecting the way your engine runs. You have a radically altered engine. The programmer may have tried to change things. The IAC opens up as RPM to prevent the engine from stalling if the throttle blades suddenly close. Maybe the programmer changed the settings. Maybe the programmer changed the throttle follower table that Rob/Shoebox mentioned. I have no way of knowing. Have you discussed these problems with the programmer?
I also don't think that the fact the "tp sensor also showed closed so thats some indication its not in the throttle linkage." is the best way to check the blades for sluggish movement. Have you physically observed the blades? Have you checked to see if they are stuck open, even slightly? Has the throttle stop screw ever been adjusted?
The pintle could be moving, but the passages may be plugged.
You seem to be suggesting the problem is my writeup. That was made specifically for a STOCK engine. Once you start changing things - stroker, cam, PCM reprogram, redirecting air to other places, aftermarket throttle body - you can't hold me responsible for what I wrote not reflecting the way your engine runs. You have a radically altered engine. The programmer may have tried to change things. The IAC opens up as RPM to prevent the engine from stalling if the throttle blades suddenly close. Maybe the programmer changed the settings. Maybe the programmer changed the throttle follower table that Rob/Shoebox mentioned. I have no way of knowing. Have you discussed these problems with the programmer?
I also don't think that the fact the "tp sensor also showed closed so thats some indication its not in the throttle linkage." is the best way to check the blades for sluggish movement. Have you physically observed the blades? Have you checked to see if they are stuck open, even slightly? Has the throttle stop screw ever been adjusted?
02-08-2013, 04:24 PM
#14
Registered User
Thread Starter
Join Date: May 2012
Location: idaho
Posts: 660
Re: what counts is the iac supposed to start and idle at?
It might not move if the pintle is stuck or damaged. You indicate you cleaned it off with a paper towel. A soft brush would have been a better choice. The factory manual cautions that moving the pintle on a used IAC valve can damage it.
The pintle could be moving, but the passages may be plugged.
You seem to be suggesting the problem is my writeup. That was made specifically for a STOCK engine. Once you start changing things - stroker, cam, PCM reprogram, redirecting air to other places, aftermarket throttle body - you can't hold me responsible for what I wrote not reflecting the way your engine runs. You have a radically altered engine. The programmer may have tried to change things. The IAC opens up as RPM to prevent the engine from stalling if the throttle blades suddenly close. Maybe the programmer changed the settings. Maybe the programmer changed the throttle follower table that Rob/Shoebox mentioned. I have no way of knowing. Have you discussed these problems with the programmer?
I also don't think that the fact the "tp sensor also showed closed so thats some indication its not in the throttle linkage." is the best way to check the blades for sluggish movement. Have you physically observed the blades? Have you checked to see if they are stuck open, even slightly? Has the throttle stop screw ever been adjusted?
The pintle could be moving, but the passages may be plugged.
You seem to be suggesting the problem is my writeup. That was made specifically for a STOCK engine. Once you start changing things - stroker, cam, PCM reprogram, redirecting air to other places, aftermarket throttle body - you can't hold me responsible for what I wrote not reflecting the way your engine runs. You have a radically altered engine. The programmer may have tried to change things. The IAC opens up as RPM to prevent the engine from stalling if the throttle blades suddenly close. Maybe the programmer changed the settings. Maybe the programmer changed the throttle follower table that Rob/Shoebox mentioned. I have no way of knowing. Have you discussed these problems with the programmer?
I also don't think that the fact the "tp sensor also showed closed so thats some indication its not in the throttle linkage." is the best way to check the blades for sluggish movement. Have you physically observed the blades? Have you checked to see if they are stuck open, even slightly? Has the throttle stop screw ever been adjusted?
02-08-2013, 05:55 PM
#15
Administrator
Join Date: Nov 1998
Location: Hell was full so they sent me to NJ
Posts: 70,825
Re: what counts is the iac supposed to start and idle at?
Get a data log in a format that we can open, and post it on an ftp site. That way we will have a better chance of sorting this out.