Cant solve rough idle
Race Director
Joined: Jan 2012
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From: United States
IF you unscrew it and spray with brake cleaner to clean the pintle and wipe it GENTLY, you should be OK. I would use a new gasket since I don't reuse those paper gaskets or my condoms.
I understand all that however, how does the DVOM tell you what the IAC is doing? All you can see is that the coils are good. Remove the pintle and the coils will still be good so you don't really know how to tell other than "The coils are good or bad", right? How do you know it is actually doing what it is supposed to be doing if you all you can tell me is the coils are good?
I understand all that however, how does the DVOM tell you what the IAC is doing? All you can see is that the coils are good. Remove the pintle and the coils will still be good so you don't really know how to tell other than "The coils are good or bad", right? How do you know it is actually doing what it is supposed to be doing if you all you can tell me is the coils are good?
Iff they are shorted, they cant either. There is a specific resistance needed to adjust accordingly. Period..
Use the Ohm section of your DVOM to look at resistance.
Its PFM.. It just does what it does, and this is the only test without a tech 1 or 2 to see wth is going on with the iac. Change ii if is bad.. Watch your idle stay steady as a rock.
Race Director
Joined: Apr 2002
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From: Anaheim CA
Measuring the coils of the IAC is about as useful as measuring the coils of the injectors. It is a very gross test that the coil is intact and doesn't tell you anything about how well the part performs.
You can do an IAC test by shorting the test terminal of the ALDL connector. That will cause the ECM to extend the IAC pintle until it bottoms out in the throttle body. The idle will go down when you do this. Part of the minimum idle adjustment.
You can do an IAC test by shorting the test terminal of the ALDL connector. That will cause the ECM to extend the IAC pintle until it bottoms out in the throttle body. The idle will go down when you do this. Part of the minimum idle adjustment.
Team Owner
Joined: Jul 2004
Posts: 28,431
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From: Hartford WI
If the coils are open, they cant do their job of opening and closing the pintle, causing the air to come in at different volumes to adjust idle accordingly..
Iff they are shorted, they cant either. There is a specific resistance needed to adjust accordingly. Period..
Use the Ohm section of your DVOM to look at resistance.
Its PFM.. It just does what it does, and this is the only test without a tech 1 or 2 to see wth is going on with the iac. Change ii if is bad.. Watch your idle stay steady as a rock.
Iff they are shorted, they cant either. There is a specific resistance needed to adjust accordingly. Period..
Use the Ohm section of your DVOM to look at resistance.
Its PFM.. It just does what it does, and this is the only test without a tech 1 or 2 to see wth is going on with the iac. Change ii if is bad.. Watch your idle stay steady as a rock.
and even though the scanner will show counts, it only shows what the ecm is telling the IAC to do, not what it actually is doing.
So, the ohm test is only a test of the IAC Coils being within spec not what it is actually doing, if anything. So if I pulled off the pintle, will the coils test out good? Absolutely. Will it work? Absolutely NOT.
Race Director
Joined: Jan 2012
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From: United States
Measuring the coils of the IAC is about as useful as measuring the coils of the injectors. It is a very gross test that the coil is intact and doesn't tell you anything about how well the part performs.
You can do an IAC test by shorting the test terminal of the ALDL connector. That will cause the ECM to extend the IAC pintle until it bottoms out in the throttle body. The idle will go down when you do this. Part of the minimum idle adjustment.
You can do an IAC test by shorting the test terminal of the ALDL connector. That will cause the ECM to extend the IAC pintle until it bottoms out in the throttle body. The idle will go down when you do this. Part of the minimum idle adjustment.
Yes you can shot the pintle out by shorting out a part of the aldl. Your point only shows the IAC goes out? Not back in? Regardless of what some think of testing the IAC, it is a step within testing and troubleshooting.
Race Director
Joined: Jan 2012
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From: United States
I see your point. What you are doing is assuming that because the ohm tests out that the coils are within spec, you assume that the pintle MUST work. If the screws are stripped or whatever, the coils can still be good but it won't extend or retract as needed.
So in this case, I was making the statement that it doesn't actually show what it is doing. It shows the coils are in good shape or not. Only way I know of seeing what the IAC is doing is to use a scanner to see what the values are and go from there. So if the scanner is at max IAC count and I open up the butterfly valve gently and it doesn't go down, I might suspect that something is wrong with the pintle. Like Cliff Harris said, it is a very crude test like the injectors. Just because the coils are good doesn't mean it is spraying the volume or pattern right.
So, the ohm test is only a test of the IAC Coils being within spec not what it is actually doing, if anything. So if I pulled off the pintle, will the coils test out good? Absolutely. Will it work? Absolutely NOT.
So in this case, I was making the statement that it doesn't actually show what it is doing. It shows the coils are in good shape or not. Only way I know of seeing what the IAC is doing is to use a scanner to see what the values are and go from there. So if the scanner is at max IAC count and I open up the butterfly valve gently and it doesn't go down, I might suspect that something is wrong with the pintle. Like Cliff Harris said, it is a very crude test like the injectors. Just because the coils are good doesn't mean it is spraying the volume or pattern right.
So, the ohm test is only a test of the IAC Coils being within spec not what it is actually doing, if anything. So if I pulled off the pintle, will the coils test out good? Absolutely. Will it work? Absolutely NOT.
A scanner, such as TTS datamaster, only shows you what the ECM is telling the IAC what it wants the IAC to do. You will not see what an IAC does unless you have a TECH 1 or Tech 2 from GM's tools of technicians, unless you own one.
And my procedure, which is from a reputable person who knows quite a bit about are cars, engines etc, is a step to troubleshoot what is wrong within a flow chart of an idle issue.
Broken pintle is a broken pintle, very common. A shorted/open coil is another part that can break in an IAC. I showed one part of the troubleshooting phase.
Also, go ahead and pull the pintle out, see if it goes back in . It will probably be broken after that as they are very fragile.
Good luck.
Team Owner
Joined: Jul 2004
Posts: 28,431
Likes: 3,284
From: Hartford WI
Assume huh? No, I wasnt assuming anything. I was looking at one part of the problem. One step at a time.
A scanner, such as TTS datamaster, only shows you what the ECM is telling the IAC what it wants the IAC to do. You will not see what an IAC does unless you have a TECH 1 or Tech 2 from GM's tools of technicians, unless you own one.
And my procedure, which is from a reputable person who knows quite a bit about are cars, engines etc, is a step to troubleshoot what is wrong within a flow chart of an idle issue.
Broken pintle is a broken pintle, very common. A shorted/open coil is another part that can break in an IAC. I showed one part of the troubleshooting phase.
Also, go ahead and pull the pintle out, see if it goes back in . It will probably be broken after that as they are very fragile.
Good luck.
A scanner, such as TTS datamaster, only shows you what the ECM is telling the IAC what it wants the IAC to do. You will not see what an IAC does unless you have a TECH 1 or Tech 2 from GM's tools of technicians, unless you own one.
And my procedure, which is from a reputable person who knows quite a bit about are cars, engines etc, is a step to troubleshoot what is wrong within a flow chart of an idle issue.
Broken pintle is a broken pintle, very common. A shorted/open coil is another part that can break in an IAC. I showed one part of the troubleshooting phase.
Also, go ahead and pull the pintle out, see if it goes back in . It will probably be broken after that as they are very fragile.
Good luck.
As I said, does it tell you much beyond the coils are ok? I don't see it. IF one feels that one needs to do that kind of work instead of agetting a real scanner to see what the ECM is doing, I suppose, a hack job is better than none.
Race Director
Joined: Jan 2012
Posts: 17,062
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From: United States
I have an Auto X-ray and a Snap On Scanner. Yes, they tell me what the command IAC numbers are. However, I can see that if the counts go up, something must happen.
As I said, does it tell you much beyond the coils are ok? I don't see it. IF one feels that one needs to do that kind of work instead of agetting a real scanner to see what the ECM is doing, I suppose, a hack job is better than none.
As I said, does it tell you much beyond the coils are ok? I don't see it. IF one feels that one needs to do that kind of work instead of agetting a real scanner to see what the ECM is doing, I suppose, a hack job is better than none.
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Team Owner
Joined: Jul 2004
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From: Hartford WI
Race Director
Joined: Jan 2012
Posts: 17,062
Likes: 166
From: United States
Team Owner
Joined: Jul 2004
Posts: 28,431
Likes: 3,284
From: Hartford WI
It is an opinion. One that is unfortunately not backed up by large sums of money and is thus placed in the circular file for review at a later date
Race Director
Joined: Apr 2002
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From: Anaheim CA
Its a gross test in the troubleshooting of a part, correct? Testing injectors is a step in finding the problem, correct?
Yes you can shot the pintle out by shorting out a part of the aldl. Your point only shows the IAC goes out? Not back in? Regardless of what some think of testing the IAC, it is a step within testing and troubleshooting.
Yes you can shot the pintle out by shorting out a part of the aldl. Your point only shows the IAC goes out? Not back in? Regardless of what some think of testing the IAC, it is a step within testing and troubleshooting.
Last edited by Cliff Harris; Aug 20, 2015 at 10:27 PM. Reason: Added clarifying language
Team Owner
Joined: Jul 2004
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From: Hartford WI
Is there a way, besides seeing other outputs from the ECM to know what the IAC is actually doing? With a TPS we can see the voltage output but not sure about IAC. Any ideas?