Idle question - JeepForum.com
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post #1 of 13 Old 12-11-2019, 05:47 PM Thread Starter
JarheadAl
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Idle question

A month or so, I replaced my IAC. Since then, if I take it out of gear and coast to a stop, the rpm stays around 1200-1300. As soon as I actually stop, it settles down to 800-900. Any ideas?

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post #2 of 13 Old 12-12-2019, 08:50 AM
mikewiz38
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Since it sounds like things were OK before you replaced the IAC so I would check the IAC. I bought an oxygen sensor once and the new one was dead out of the box.

To test the IAC sounds a bit complicated but this post makes it sound like it's possible...

https://www.jeepforum.com/forum/f13/.../#post40446689

And finally, I don't know if you have a scan tool or access to one, but I made a document from my scan tool with a bunch of data, one of them being the IAC motor position. I'm guessing if you can see it change then things are working properly.

https://docs.google.com/document/d/1...it?usp=sharing

And then last but not least... When I was writing up my document about the scan tool, I came across this youtube video that talks a bit about how to test it. It may be helpful.


Good Luck!

1994 Wrangler YJ - 4.0L - 5 Speed
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post #3 of 13 Old 12-12-2019, 03:53 PM
bpounds
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Might be normal. A smog control feature. Typically more when the engine is warming up.

Bill

1988 Wrangler,4.2L I-6, Howell EFI JP-1,CRT HEI Ign,AX15 ext slave conversion, Zone 2" lift + 1" BL + 1/2" booms, BFG 31 x 10.5, Bestop.
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post #4 of 13 Old 12-12-2019, 05:31 PM Thread Starter
JarheadAl
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Well, when I replaced my IAC, there was no IAC. There was a wire nuts wrapped in electrical tape with a piece of rubber behind a homemade delete plate. I will read the thread about testing the IAC.
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post #5 of 13 Old 12-12-2019, 05:55 PM
Boojo35
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I could type a zillion word post as to why I think it may be normal. (and I am known for long posts) LOL>

I really think that it is probably normal.
Chrisnvegas likes this.

If you cannot fix it with a hammer then it has to be an electrical problem.
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post #6 of 13 Old 12-12-2019, 07:45 PM Thread Starter
JarheadAl
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If you're willing to teach, I'm willing to learn.
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post #7 of 13 Old 12-13-2019, 06:59 AM
bruinjeeper
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Quote:
Originally Posted by JarheadAl View Post
Well, when I replaced my IAC, there was no IAC. There was a wire nuts wrapped in electrical tape with a piece of rubber behind a homemade delete plate. I will read the thread about testing the IAC.
What the hell? Why?

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post #8 of 13 Old 12-13-2019, 07:58 AM Thread Starter
JarheadAl
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Who knows why an OP does the weird things they do. How long does it take to drive to the local autoparts store versus the in-depth thought process that resulted in this then add the time to make the delete plate?
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post #9 of 13 Old 12-13-2019, 05:26 PM
Boojo35
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Quote:
Originally Posted by JarheadAl View Post
If you're willing to teach, I'm willing to learn.
Why?

I started in this business when breaker points and condensers were the norm. I have learned other systems along the way in progression. C3I or computer controlled carbs, TBI, MPFI, DFI, and a lot of variations on the way.

A lot of it is manufacturer specific and just makes you dumber in a lot of peoples eyes on a forum. JS.

If you cannot fix it with a hammer then it has to be an electrical problem.
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post #10 of 13 Old 12-13-2019, 06:21 PM
Chrisnvegas
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All our FI YJ's do it. Even TJ's do it.
I'll check my car tonight.

On mine:
The idle is a little elevated, but not high. Maybe 850 or 900? I'll check this weekend.
Come to a complete stop, immediately drops to 750.

A long time ago someone told me why. I THINK he said something like, the PCM knows your moving from the VSS.
It adjusts the FI from the MAP or MAF while you are driving but doesn't consider the idle because you are still driving. Even though the TPS is closed, while you are driving it's not at 750 rpm. So it keeps everything adjusted according to the MAP or MAF.

When you stop, it considers the idle speed and adjusts accordingly for being at a stop.

NOTE: This is from my brain, trashed by years of alcohol abuse, smoking stuff, I was even kicked in the head by a horse.
This is not to be considered a fact.

"Alferd Packer: “Stand up, you voracious, man-eating son of a *****, stand up! There was seven democrats in Hinsdale County and you up and ate five of them."
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post #11 of 13 Old 12-13-2019, 08:36 PM
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My car does the same thing

"Alferd Packer: “Stand up, you voracious, man-eating son of a *****, stand up! There was seven democrats in Hinsdale County and you up and ate five of them."
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post #12 of 13 Old 12-14-2019, 09:21 AM Thread Starter
JarheadAl
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Quote:
Originally Posted by Chrisnvegas View Post
My car does the same thing
But does your JEEP do it? JK. Thanks, that explains it as much as I would understand.
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post #13 of 13 Old 12-14-2019, 09:33 AM
Chrisnvegas
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Quote:
Originally Posted by JarheadAl View Post
But does your JEEP do it? JK. Thanks, that explains it as much as I would understand.
Yes, both mine and my friend's Jeep does it. When I discovered it, a few years ago, I asked him. We went for a ride in his Jeep, his also kept the idle elevated till it completely stopped. So last night I tested my car.
Coming up to a red light, I put it in neutral and coasted. Yep, stayed around 1100 rpm until a complete stop, then dropped as soon as I stopped.

For some reason, this seems "normal?"

"Alferd Packer: “Stand up, you voracious, man-eating son of a *****, stand up! There was seven democrats in Hinsdale County and you up and ate five of them."
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