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Discussion Starter · #1 ·
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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Discussion Starter · #11 ·
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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Discussion Starter · #15 ·
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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