IAC issues, help plz - JeepForum.com
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post #1 of 16 Old 03-12-2016, 02:46 PM Thread Starter
svshaw82
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Hey guys! Engine specs, 1989 4.0 renix. Ive replaced my IAC, clean it thoroughly and the throttle body. I'm experiencing a high random idle that goes over 2000 RPMs. The only solution I've been able to find is wait for the IAC to catch up with the idle and unplug it. That's been the only way to control it so far.

Is there anything in the wiring harness that I can check for? I've gone through 3 IACs now. All of them have the same result and it just happened out of nowhere.

Since I rebuilt the engine I went through my wiring harness and got rid of all the ground blocks, and gave each circuit a dedicated ground to the firewall. Engine has been broken in for about fifteen hundred miles, so far all was well until a few weeks ago. Sometimes it starts normally sometimes it starts at over 2000 RPM, and once it goes over that range it will not come down. I've only been able to get it to come down after turning the engine on and back off several times, and then I unplug the IAC once idle is normal.

Are there any specific voltages to certain wires that I can check for, or ohm readings? Any help is much appreciated thank you!

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post #2 of 16 Old 03-12-2016, 02:51 PM
PimaXJ
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There is a way to test the IAC a least on the newer 4.0. Do a search.
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post #3 of 16 Old 03-12-2016, 03:00 PM Thread Starter
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Originally Posted by PimaXJ View Post
There is a way to test the IAC a least on the newer 4.0. Do a search.
Brand new out the box same symptoms as old one? You think I have bad IAC?
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post #4 of 16 Old 03-12-2016, 10:13 PM
ECL
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Is there a throttle position sensor on that year? Might be worth checking.
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post #5 of 16 Old 03-12-2016, 11:42 PM Thread Starter
svshaw82
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The TPS is only a few years old
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post #6 of 16 Old 03-12-2016, 11:54 PM
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The TPS is only a few years old
That doesn't mean it couldn't have went bad since

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post #7 of 16 Old 03-14-2016, 08:00 PM
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Sounds like bad TPS.

Test it. Tip 8 in my link below.

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post #8 of 16 Old 03-14-2016, 11:57 PM Thread Starter
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Sounds like bad TPS.

Test it. Tip 8 in my link below.
No link shown bud
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post #9 of 16 Old 03-15-2016, 01:59 AM
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No link shown bud
Its part of his signature

http://cruiser54.com/

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post #10 of 16 Old 03-15-2016, 08:28 AM
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Maybe it doesn't show on the App?

http://cruiser54.com/?p=54

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post #11 of 16 Old 03-21-2016, 07:06 AM Thread Starter
svshaw82
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Think i figured out the issue. During motor rebuild i went though my wiring harness. Cutout all ground blocks and extended all grounds to the firewall.

The big copper lug i used had corroded a little and was loose. Sanded, wire brushed, greased it, and retorqued it.

Problem dissappeared. :-)
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post #12 of 16 Old 03-21-2016, 07:54 AM
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Those grounds aren't important.........LOL.

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post #13 of 16 Old 03-21-2016, 08:25 AM Thread Starter
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Those grounds aren't important.........LOL.
Lol well I didn't suspect the lug at first because I used dielectric grease when I made the connector. Then wrapped it with electrical tape. It wasn't until the engine was at a high idle I grabbed it. When I moved it slightly the idle came back down. Lol
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post #14 of 16 Old 03-21-2016, 08:36 AM
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Thanks for reporting back. There's a better product or 2, which are conductive and lock out air. One is NoAlOx.

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post #15 of 16 Old 03-25-2016, 03:32 PM Thread Starter
svshaw82
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Thanks Cruzer. Might be putting a new lug on after our big bear trip. Although it was a solid copper lug, and crimped on with a big wrench. Also used an old battery cable to run a second ground off the same lug to the intake manifold.

So I have battery ground to the block, battery ground to the body, firewall grounds for all injectors and sensors, and firewall ground to intake manifold. Should cover everything right?
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