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  #1  
Old 05-21-2019, 06:47 PM
Harbor_Handed Harbor_Handed is offline
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Default Straight talk about Idle Air Control Valves (IAC)

I believe that many IAC valves -- even new ones from Motorcraft -- sometimes have issues with not putting the idle speed exactly where it's supposed to be. Here is my story:

My truck had occasional low idling. It would sometimes idle where it's supposed to, around 900 RPM, and other times it would drop down to 600 RPM and just sit there.

People said, "Clean the IAC" so I did, and it usually improves. For a short time.

Last year, I replaced original IAC valve with a Motorcraft one from Rock Auto, but it would still occasionally idle very low. So I sent it back as defective and they sent me a new one.

The new one would also occasionally idle very low. I clean it, even though it's not "gummed up," by spraying throttle body cleaner and going at it with a Q-tip to really remove the very thin haze of carbon...and it improves, likely due to the slight residue of lubrication the throttle body cleaner leaves behind.

But the RPMs still dip down to 600 sometimes when coming to a stop or slowing way down, but the IAC will bump them back up....until it doesn't anymore, and it starts STAYING low again. Then it's time for another round of cleaning the IAC, even though it's only been 1K or so miles.

I'm a compulsive RPM watcher so I always know exactly how my truck is idling.

Well, I've recently gotten sick and tired of this issue with the Motorcraft IAC valves (I've tried three so far counting the original), and decided I'd like to try an aftermarket brand to see if that would fix the low idle thing once and for all.

I bought the Duralast IAC valve from Autozone, and put it on there. It was wonderful. The RPMs would never drop down low to 600 when coming to a stop like the Motorcraft would, the RPMs always stayed up around 900. Love that!!
However...the Duralast IAC valve would occasionally surge the idle up to 1500 when I put it in Park/Neutral! It does this at warm idle about 1/3 of the time - bumps up the idles way up to 1500 and just stays there, high-idling away. Not good.

I took the Duralast IAC valve back today for a refund. I do not believe there is a vacuum leak in my truck causing idle weirdness because it's all intermittent -- not consistent. IAC and throttle body are both very clean inside. I assume it is these IAC valves that are not performing correctly 100% of the time.

So just to review...my Motorcraft IAC valve occasionally drops my idle way too low and sometimes stays there. And my Duralast IAC occasionally bumps my idle up way too high in Park/Neutral and stays there.

I don't like how the Motorcraft IAC valves occasionally drop the RPMs down to 600 when coming to a stop or slow down, even if it does bump it up after a second to 900 RPM. Is it normal for it to allow that type of momentary drop?

Should I head to Napa and try the Echlin IAC valve?

I welcome any thoughts!
__________________
2003 Mazda B2300
2.3 L DOHC
4 Cylinder, Automatic Transmission
168,000 miles on Odometer as of Mar 2020
25 mpg on mixed hwy/city driving


Last edited by Harbor_Handed; 05-22-2019 at 01:05 AM.
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  #2  
Old 05-21-2019, 11:02 PM
Dirtman Dirtman is offline
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Default Re: Straight talk about Idle Air Control Valves (IAC)

Before you keep tossing IAC valves on it, verify the commanded rpm vs actual rpm. If the commanded value matches the actual then there's nothing wrong with the IAC valve, its just doing what the computer is telling it. Start by clearing the keep alive memory and performing an idle relearn procedure.
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  #3  
Old 05-22-2019, 12:59 AM
Harbor_Handed Harbor_Handed is offline
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Default Re: Straight talk about Idle Air Control Valves (IAC)

Quote:
Originally Posted by Dirtman View Post
Before you keep tossing IAC valves on it, verify the commanded rpm vs actual rpm. If the commanded value matches the actual then there's nothing wrong with the IAC valve, its just doing what the computer is telling it. Start by clearing the keep alive memory and performing an idle relearn procedure.
Thank you.
I have unhooked neg. battery cable & done idle relearn procedure in the past, and it does seem to help the low idling for a while. But then it will come back again after a while.

If it was the computer giving a low commanded value when it drops to 600 w/ Motorcraft IAC valve, then why wouldn't the Duralast IAC valve also drop RPMs low like that? The Duralast IAC kept the RPMs right around 900 which was perfect...however the RPMs would sometimes surge with the Duralast and stay at 1500 when put into Park/Neutral, which it never did with the Motorcraft IAC installed.

Don't these different results imply that the problem is the IAC valves and not the truck's computer?
__________________
2003 Mazda B2300
2.3 L DOHC
4 Cylinder, Automatic Transmission
168,000 miles on Odometer as of Mar 2020
25 mpg on mixed hwy/city driving


Last edited by Harbor_Handed; 05-22-2019 at 01:06 AM.
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  #4  
Old 05-22-2019, 04:49 AM
tomw0 tomw0 is offline
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Default Re: Straight talk about Idle Air Control Valves (IAC)

Have you ever cleaned out the intake manifold? The PCV system dumps crankcase vapors into the intake, and generally coats the inside with oily residue. Open the throttle and look inside and you won't see clean metal...
The area behind the throttle plate can also get coated with PCV crud. It may interfere with throttle operation and affect idle speed.
I suggest using come cleaner that won't kill your catalytic converter(s) to clean the throttle plate, the area immediately behind the throttle plate, and the inner surface of the intake manifold in general. Flush it out so it is fairly clean. PBT, start the engine, and watch the cloud of cleaner as it gets combusted(for a few minutes, tops).
I suggest you will have a lot more responsive throttle, and the idle will settle down.
FWIW, the first design had the IAC out by the air cleaner, right behind the grill. It did not respond so well to commands. It worked, but was a bit more sensitive than even yours. It doesn't need cleaning as often, but when the intake & throttle plate get goo'd, it cannot compensate as well .. for some reason. Mine used to die 3-5 times on a cold start, for years, until I gave the intake 'the flush' treatment. It now starts, and keeps running without stalling. OTOH, when I get it good and warm, and go into Home Depot for a few minutes, it wants to stall when I restart hot. Maybe it needs cleaning again?
tom
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  #5  
Old 05-22-2019, 09:51 AM
Harbor_Handed Harbor_Handed is offline
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Default Re: Straight talk about Idle Air Control Valves (IAC)

Quote:
Originally Posted by tomw0 View Post
Have you ever cleaned out the intake manifold? The PCV system dumps crankcase vapors into the intake, and generally coats the inside with oily residue. Open the throttle and look inside and you won't see clean metal...
The area behind the throttle plate can also get coated with PCV crud. It may interfere with throttle operation and affect idle speed.
I suggest using come cleaner that won't kill your catalytic converter(s) to clean the throttle plate, the area immediately behind the throttle plate, and the inner surface of the intake manifold in general. Flush it out so it is fairly clean. PBT, start the engine, and watch the cloud of cleaner as it gets combusted(for a few minutes, tops).
I suggest you will have a lot more responsive throttle, and the idle will settle down.
FWIW, the first design had the IAC out by the air cleaner, right behind the grill. It did not respond so well to commands. It worked, but was a bit more sensitive than even yours. It doesn't need cleaning as often, but when the intake & throttle plate get goo'd, it cannot compensate as well .. for some reason. Mine used to die 3-5 times on a cold start, for years, until I gave the intake 'the flush' treatment. It now starts, and keeps running without stalling. OTOH, when I get it good and warm, and go into Home Depot for a few minutes, it wants to stall when I restart hot. Maybe it needs cleaning again?
tom
Thank you for the reply.

The intake manifold is new, installed by master technician at dealership less than 20k miles ago. He also did induction cleaning of throttle body, and I have also cleaned the throttle body myself since then, although it wasn't dirty at all. There is no carbon or gunk at all upstream of the throttle plate.

The IAC valves I've tried, the throttle body, the intake manifold...all of them are clean enough to eat off of.
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2003 Mazda B2300
2.3 L DOHC
4 Cylinder, Automatic Transmission
168,000 miles on Odometer as of Mar 2020
25 mpg on mixed hwy/city driving

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  #6  
Old 05-23-2019, 03:28 PM
Harbor_Handed Harbor_Handed is offline
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Default Re: Straight talk about Idle Air Control Valves (IAC)

Update:
I have my Motorcraft IAC valve in the truck right now, and today when I put it in Park, it dropped the idles low to 600 and just hung there. I got out and pulled the IAC wire off to see what would happen, and the truck immediately died.

I then reconnected IAC wire, and started the truck, and it idled fine at 900 where it's supposed to be.

I suspect the issue that causes the Motorcraft IAC to hang at 600 RPM is the same issue that caused the Duralast IAC to overcompensate and bump idle up to 1500.

I wonder what the issue could be? Failing Throttle Position Sensor, maybe? But I get good MPG and have no CEL...

I will keep updating this thread as I continue my IAC journey, for anyone else in the future who is having similar problems. Hopefully I will eventually figure out the issue and find a fix.
__________________
2003 Mazda B2300
2.3 L DOHC
4 Cylinder, Automatic Transmission
168,000 miles on Odometer as of Mar 2020
25 mpg on mixed hwy/city driving


Last edited by Harbor_Handed; 05-23-2019 at 03:31 PM.
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  #7  
Old 05-23-2019, 04:48 PM
bullygrip bullygrip is offline
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Default Re: Straight talk about Idle Air Control Valves (IAC)

are you using a new gasket on that valve? im no mechanic but there is also a "intake manifold runner control valve" that could possibly cause erratic idles, though they say it should set of the mil light. its vacuum controlled , so you can at least check the vacuum lines, and its a cheap part.

Last edited by bullygrip; 05-23-2019 at 05:07 PM.
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  #8  
Old 05-23-2019, 07:49 PM
Harbor_Handed Harbor_Handed is offline
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Default Re: Straight talk about Idle Air Control Valves (IAC)

Quote:
Originally Posted by bullygrip View Post
are you using a new gasket on that valve? im no mechanic but there is also a "intake manifold runner control valve" that could possibly cause erratic idles, though they say it should set of the mil light. its vacuum controlled , so you can at least check the vacuum lines, and its a cheap part.
Thanks, bullygrip.
I did not replace the gasket but the rubber gasket is in great condition. The Duralast IAC valve came with a paper gasket, which I used on that.

Regarding vacuum controlled runner valve, my understanding is that if my issue was vacuum related, then it would be consistent. But it doesn't happen consistently, it's very intermittent.

I'm going to buy a new throttle position sensor in the next few days, and see if that eliminates the weird idle problems once and for all.
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2003 Mazda B2300
2.3 L DOHC
4 Cylinder, Automatic Transmission
168,000 miles on Odometer as of Mar 2020
25 mpg on mixed hwy/city driving

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  #9  
Old 05-24-2019, 02:39 AM
bullygrip bullygrip is offline
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Default Re: Straight talk about Idle Air Control Valves (IAC)

well the branded valves are probably made in china, and there are some cheap valves on ebay. but if you have a number of valves lying around, Ide dunk one in a clothing detergent solution for 20 or 30 minutes then work that valve up and down manually, then rinse and let completely dry. thats all i got sorry.
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Old 05-24-2019, 04:23 PM
Harbor_Handed Harbor_Handed is offline
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Default Re: Straight talk about Idle Air Control Valves (IAC)

Quote:
Originally Posted by bullygrip View Post
well the branded valves are probably made in china, and there are some cheap valves on ebay. but if you have a number of valves lying around, Ide dunk one in a clothing detergent solution for 20 or 30 minutes then work that valve up and down manually, then rinse and let completely dry. thats all i got sorry.
Hi, if you're talking about IAC valves, I don't have any lying around, I just have my one Motorcraft one installed in my truck. The Duralast one I took back days ago, due to high idle in Park/Neutral.

I bought a new throttle position sensor today and installed it. The idles acted normal on the drive home. Hope it keeps up, and that this was the solution to my idle problems.

Happy Memorial Day weekend
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2003 Mazda B2300
2.3 L DOHC
4 Cylinder, Automatic Transmission
168,000 miles on Odometer as of Mar 2020
25 mpg on mixed hwy/city driving

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  #11  
Old 05-28-2019, 04:44 PM
Harbor_Handed Harbor_Handed is offline
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Default Re: Straight talk about Idle Air Control Valves (IAC)

Just a quick update:
Since installing the new TPS, I have not had any hanging idles.
Once in a while, when slowing down to turn or coming to a stop, the RPMs will momentarily dip down to 600 RPM but they always bump back up to 900 RPM. Hoping this keeps up.

As I mentioned, I think the Motorcraft IAC valves -- the ones I have had in my truck -- allow the RPMs to momentarily dip down to 600 sometimes when slowing/stopping. I consider it just a quirk of these Motorcraft IAC valves. As I mentioned, the Duralast IAC I had in there was more vigilant and did not allow to ever drop low like that. But I don't think it's abnormal or "bad" as long as it gets bumped back up to where it should be after a second.

Will keep updating this thread with any new idling developments. So far, it's looking like the new TPS fixed my occasional low, hanging idle issue.
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2003 Mazda B2300
2.3 L DOHC
4 Cylinder, Automatic Transmission
168,000 miles on Odometer as of Mar 2020
25 mpg on mixed hwy/city driving

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  #12  
Old 06-08-2019, 02:51 PM
turismolover22 turismolover22 is offline
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Default Re: Straight talk about Idle Air Control Valves (IAC)

Reset base idle and the 600 RPM drop should go away, permanently.

Essentially you force the ECU to close the IAC (needs to be clean) then you adjust the base idle screw on your throttle body to be set at whatever idle you want it to be. It can never get "lower" than that as it will be (at the time of the reset procedure) to be the only source of air intake in the system.

I can explain in greater detail how to do this if you are interested, but I wanted to give the abridged version first.
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  #13  
Old 06-08-2019, 05:23 PM
Dirtman Dirtman is offline
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Default Re: Straight talk about Idle Air Control Valves (IAC)

Yea... fuck with the screw of death... good luck.
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  #14  
Old 06-08-2019, 06:51 PM
turismolover22 turismolover22 is offline
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Default Re: Straight talk about Idle Air Control Valves (IAC)

Quote:
Originally Posted by Dirtman View Post
Yea... fuck with the screw of death... good luck.
Screw of death? Care to explain your fear of a throttle body?
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  #15  
Old 06-15-2019, 12:04 PM
Harbor_Handed Harbor_Handed is offline
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Default Re: Straight talk about Idle Air Control Valves (IAC)

Quote:
Originally Posted by turismolover22 View Post
Reset base idle and the 600 RPM drop should go away, permanently.

Essentially you force the ECU to close the IAC (needs to be clean) then you adjust the base idle screw on your throttle body to be set at whatever idle you want it to be. It can never get "lower" than that as it will be (at the time of the reset procedure) to be the only source of air intake in the system.

I can explain in greater detail how to do this if you are interested, but I wanted to give the abridged version first.
So, you're saying the reason my RPMs sometimes dip down to 600 when slowing way down or stopping...is because, at some point in its history, the idle screw has been tampered with?

Yes, please explain in more detail what to do. If the screw has been messed with causing the RPMs do dip down low, then I wish to restore it to the default setting. Thank you.
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2.3 L DOHC
4 Cylinder, Automatic Transmission
168,000 miles on Odometer as of Mar 2020
25 mpg on mixed hwy/city driving

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