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I have seen reference in this forum to cleaning out the IAC to help fix rough idle. - When I look in my chilton manual I do not see 'IAC' anywhere. What exactly is it and how do I clean it. Thanks.
 

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The idle air controller is what meters air into the engine through the throttle body when the engine is at idle RPMs when the butterfly valve is closed (which is closed whenever your foot is off the accelerator pedal).

It's held onto the throttle body via two T-25 (maybe T-20) bolts on the engine-side of the throttle body. I don't doubt the Chilton's manual doesn't cover it well, I consider Chilton's and Hayne's manuals little better than nothing.

Remove the IAC via those two screws and then clean its solenoid actuated plunger gently with aerosol throttle body cleaner and a toothbrush. Use a small brush like a baby bottle brush to also clean the oriface (opening) the plunger fits into which is how the air gets into the throttle body. If either is dirty, air can have trouble getting into the engine when the engine is idling. :)
 

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iac wouldn't cause a rough idle,could cause a low idle or high idle.All it does is control idle air flow into the engine.
 

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Jerry, that image is great. Would have helped out a ton when I cleaned mine for the first time a few weeks ago! And Chilton and Haynes (although vague and misrepresented for most models) helped me do a lot of routine maint stuff before I found this forum.
 

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Nonya said:
iac wouldn't cause a rough idle,could cause a low idle or high idle.All it does is control idle air flow into the engine.
That depends entirely on what the OP and you are calling a rough idle. Unsteady RPMs might be a rough idle to one person while another would only term a misfire as a rough idle. I call 'em both a rough idle... but that's just me. My latest rough idle experience occurred in my wife's 2001 Grand Cherokee and it was cured when I cleaned its IAC. I first gave it to the dealer to fix under warranty & suggested they clean the IAC as a fix... but they insisted it couldn't be the IAC causing the problem as you do... and said it required a $200 throttle body cleaning and fuel injector service. I told 'em to shove it and fixed it in 15 minutes that Saturday by cleaning the IAC. :)
 

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Well i guess if it was that dirty it could mess with the computers ability to set it position and cause a very odd idle.I've never had to clean mine but i use Lucas fuel system treatment in every tank,seems to keep everything clean in the intake.I started using it my my wifes firebird because the idle was high and low,cleared it up and no more weirdness.My jeep has very high mileage 165k plus and the iac doesn't give me any trouble so far.NOW THAT I POSTED ABOUT IT,it will LOL
 

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Jerry Bransford said:
That depends entirely on what the OP and you are calling a rough idle. Unsteady RPMs might be a rough idle to one person while another would only term a misfire as a rough idle. I call 'em both a rough idle... but that's just me. My latest rough idle experience occurred in my wife's 2001 Grand Cherokee and it was cured when I cleaned its IAC. I first gave it to the dealer to fix under warranty & suggested they clean the IAC as a fix... but they insisted it couldn't be the IAC causing the problem as you do... and said it required a $200 throttle body cleaning and fuel injector service. I told 'em to shove it and fixed it in 15 minutes that Saturday by cleaning the IAC. :)
If I was a Jeep tech and had you come walking into the shop and tell me what you thought the Jeep needed, I think I would listen. Of course, I have observed you helping people for years on JeepForum & Quadratec forum and every once in a while, I see you on other boards. When Jerry Bransford speaks, you best listen. :2thumbsup:
 

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Well i guess if it was that dirty it could mess with the computers ability to set it position and cause a very odd idle.I've never had to clean mine but i use Lucas fuel system treatment in every tank,seems to keep everything clean in the intake.I started using it my my wifes firebird because the idle was high and low,cleared it up and no more weirdness.My jeep has very high mileage 165k plus and the iac doesn't give me any trouble so far.NOW THAT I POSTED ABOUT IT,it will LOL
I'm missing something and I need your guidance. If the Jeep in question, 1998, is FI, how does the Lucus fuel system treatment get to the parts on the TB to clean them?
 

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I've never had to clean mine but i use Lucas fuel system treatment in every tank,seems to keep everything clean in the intake.
Considering that not much more than air flows through the intake manifold on a fuel injected engine, the is no chance that a fuel additive is going to do much cleaning around the throttle body or IAC.
 

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The idle air controller is what meters air into the engine through the throttle body when the engine is at idle RPMs when the butterfly valve is closed (which is closed whenever your foot is off the accelerator pedal).

It's held onto the throttle body via two T-25 bolts on the engine-side of the throttle body. I don't doubt the Chilton's manual doesn't cover it well, I consider Chilton's and Hayne's manuals little better than nothing.

Remove the IAC via those two screws and then clean its solenoid actuated plunger gently with aerosol throttle body cleaner and a toothbrush. Use a small brush like a baby bottle brush to also clean the oriface (opening) the plunger fits into which is how the air gets into the throttle body. If either is dirty, air can have trouble getting into the engine when the engine is idling. :)
On my 2006 Sport. 6 speed manual tranny, 4 liter, my IAC valve does NOT look like the one you are showing Jerry. It LOOKS like my IAC is actually part of the throttle body and after removing the electrical connect, I can not finds the screws that MIGHT hold it to the T/B.

I am having the same idle increase up to about 1500 Revs and after the clutch is pushed in to change gears and still driving down the road. The revs will actually go up to about 3000 which can be quite unnerving as you may imagine!

Do I have to replace the whole throttle body to replace/repair MY IAC?

Thanks for any help.....
 

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Considering that not much more than air flows through the intake manifold on a fuel injected engine, the is no chance that a fuel additive is going to do much cleaning around the throttle body or IAC.
You might think that but think carefully...how to you think those passages and different parts get carboned up if only air runs through them?

That manifold is wet ..yes wet with fuel even though its fuel injected.That fuel combusts in the manifold and Waa-LAA carbon all over everything.Trust me on this,my jeep has 170k thous miles on it and if you lookat my manifold ,iac etc it looks clean like brandnew.The guy that changed my exhaust manifold couldn't get over how it looked new inside.His 99 with 80k on it was caked with carbon.

Lucas fuel treatment is one of the few products i've tried over the years that really worked.

ps my 99 firebird has 113k thous miles on it and same thing,iac never been touched etc.we use lucas in that too.
 

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That fuel combusts in the manifold

Well it doesn't exactly combust in the manifold. It only combusts when it is ignited which happens in the cylinder under compression.
But we know what you mean.
 

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That fuel combusts in the manifold

Well it doesn't exactly combust in the manifold. It only combusts when it is ignited which happens in the cylinder under compression.
But we know what you mean.
Ok if it doesn't combust in the intake then please explain the combustion by products in the intake and iac etc.Inquiring minds want to know:)
 

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Maybe it's blow-by coming through your crankcase breather?
Maybe or are you sure?How does the blowby cause the iac passages to get carboned up?

The manifold has constant combustion taking place in it but the open cylinders are constantly pulling it back in.Also the intake valves leak a little combustion intro the intake system.Like i said its a wet system and lucas will keep the iac clean.Sure makes mine trouble free.
 

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The manifold has constant combustion taking place in it but the open cylinders are constantly pulling it back in.
Don't you think your intake manifold would run a little hotter than it does if this were the case?

No offense, but it sounds like you don't have a very firm grasp on how internal combustion engines work.
 

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Don't you think your intake manifold would run a little hotter than it does if this were the case?

No offense, but it sounds like you don't have a very firm grasp on how internal combustion engines work.
Yeah i just learning about them...please tell me more.
 
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