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IAC sticking open?

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Old 07-28-2012, 12:07 PM   #1
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IAC sticking open?

Hey guys, my daily is a 98 4.3 5spd reg cab short box, this problem really isn't hurting anything but is just more of a nuisance than anything.

Anyways, if i push the clutch in coming to a stop, the truck takes a while to rev down, also if im just cruising along, say in 3rd and I take my foot off the gas as if to let it engine brake, it will keep driving along at ~1500rpm problem free.

I've cleaned the throttle body and plate, and it works very freely and closes all the way, that is why I'm leaning towards a potentially lazy IACV.

Has anyone had a similar issue?
Old 07-28-2012, 12:44 PM   #2
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Re: IAC sticking open?

I believe it's a common problem with the 4.3 5 speeds. Something about the tune if I recall correctly. I think crew cab sonoma made a stopper to prevent the iac from opening so much.


Though, if it's something that's recently happened it could be a lazy iac.
Old 07-28-2012, 01:23 PM   #3
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Re: IAC sticking open?

It seems to be continually getting worse, I've owned the truck for a few months and don't recall it ever doing it when I first bought it.
Old 07-31-2012, 03:53 AM   #4
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Re: IAC sticking open?

This is just a stab but it could be your throttle position sensor I'm having a similar problem. My truck 4.3l 1991 s10 is a cold starter now and once it's hot it idles to about 1500 rPms when I put it in neutral. Mine is a touch worse because sometimes the idle is sorta high and sometimes it's like 2500 Rpms. I still haven't tracked mine down yet but I just got done reading up on it and I believe it is the throttle position sensor I'm just gunna replace mine tomarrow oreilly has it for 50 bucks..... eBay has it for 10 if you know which one let me know of you sOlve it I have a similar problem!
Old 07-31-2012, 01:15 PM   #5
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Re: IAC sticking open?

Quote: Originally Posted by beandip
I believe it's a common problem with the 4.3 5 speeds. Something about the tune if I recall correctly. I think crew cab sonoma made a stopper to prevent the iac from opening so much.


Though, if it's something that's recently happened it could be a lazy iac.
It cant be that common, I have never had that issue.

I would check the IAC, TPS and throttle plate. If the throttle plate is not fully closing or the hole for the diffuser is bigger than normal then it will rev high.
Old 07-31-2012, 01:42 PM   #6
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Re: IAC sticking open?

it is a common complaint from manual
tranny equipped 4.3 owners.

been many threads about it started on here.
Old 07-31-2012, 06:52 PM   #7
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Re: IAC sticking open?

i just fixed my problem today! it was the iac! it malfunctioned and it got stuck too far out! make sure the iac isnt out more than 1 and an eighth inch. when u measure it include from the bottom of the threads to the pointed tip of it. i wiggled mine all they way down and my trucks idleing like a dream now.
Old 08-01-2012, 03:39 PM   #8
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Re: IAC sticking open?

Quote: Originally Posted by bur burb
i just fixed my problem today! it was the iac! it malfunctioned and it got stuck too far out! make sure the iac isnt out more than 1 and an eighth inch. when u measure it include from the bottom of the threads to the pointed tip of it. i wiggled mine all they way down and my trucks idleing like a dream now.
wow, i wish mine was that easy to fix. i tried two new IAC's before I realized it is in the programming. I mean, why would it only stick open when coming to a stop? My rpms hang until my speedo reaches zero and then immediately drop. Only the computer would care or know when I was completely stopped.
Old 08-01-2012, 03:40 PM   #9
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Re: IAC sticking open?

Quote: Originally Posted by bubba68ss
wow, i wish mine was that easy to fix. i tried two new IAC's before I realized it is in the programming. I mean, why would it only stick open when coming to a stop? My rpms hang until my speedo reaches zero and then immediately drop. Only the computer would care or know when I was completely stopped.
edit: just read your last post. seems you are having a completely different problem
Old 08-02-2012, 11:57 PM   #10
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Re: IAC sticking open?

Quote: Originally Posted by bur burb
i just fixed my problem today! it was the iac! it malfunctioned and it got stuck too far out! make sure the iac isnt out more than 1 and an eighth inch. when u measure it include from the bottom of the threads to the pointed tip of it. i wiggled mine all they way down and my trucks idleing like a dream now.
Thanks a lot man, gonna pull it off tomorrow, clean it and give it a quick measure. It's starting to drive me bonkers, feels like I have cruise control on all the time.
Old 08-04-2012, 03:39 AM   #11
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Re: IAC sticking open?

Quote: Originally Posted by Wybrow
Thanks a lot man, gonna pull it off tomorrow, clean it and give it a quick measure. It's starting to drive me bonkers, feels like I have cruise control on all the time.
Let me know if it solves the problem cause my trucks still running great!!
Old 08-06-2012, 12:00 PM   #12
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Re: IAC sticking open?

Well, I pulled my IAC out, cleaned the bore inside the TB and the IAC itself. I pushed the IAC tip in and re-installed it. Did an IAC learn on the truck and it ran like a dream for a couple days. I thought I was out of the woods, but now it is doing it again, but definitely no where near as bad.
Old 08-07-2012, 02:34 AM   #13
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Re: IAC sticking open?

Mine did the same thing. I replaced
My iac 6 months before i had that problem. It turned out that the old one worked perfectly still. So I took out the new one with the problem and put the old one back in. I don't know how they move but I have a feeling mine went out and didn't go back in. I would buy a new one and push it all the way in and call it a day. If you DONT want to buy one a good way to test it is to unplug it and tuck it outa the way and go for a drive. Without an iac the idle relies on the throttle stop screw. If the problem stops while the iac is unplugged then just replace the iac. Goodluck!! Lemme know how it goes!!
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