99 tj 4.0 low idle/ wont idle when cold - JeepForum.com
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post #1 of 4 Old 01-09-2014, 08:03 PM Thread Starter
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1999 TJ Wrangler 
Join Date: Jan 2014
Location: oregon city
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99 tj 4.0 low idle/ wont idle when cold

So I finally bought my first wrangler and I'm trying to get it dialed in now. Currently i am having trouble with the idle. It will sit at the first notch around 300 rpm. It doesn't run rough but when the motor is cold i have to hold the axcel down for a few minutes or it will die.

So here is some background.
When I bought it a few weeks ago it ran fine but the idle would jump around from 1200 to 2000 rpm. I took throttle body off and cleaned it, the IAC, and all of the connecting hoses with Seafoam. this didn't really change much. So then I replaced the IAC all together and now it idles way too low. I've changed the plugs(which were in the worst condition I've ever seen) and the cap and rotor as well. I am currently running Seafoam through the fuel.

is it an issue with the computer or maybe the plug that changes the IAC position? because when i switch the two back and forth the idle will be either way high or way low like the IAC isnt even being moved.

I'm getting a little annoyed with it now and i need some help so
thanks for the help in advance!

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post #2 of 4 Old 02-01-2014, 05:49 PM
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1997 TJ Wrangler 
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Location: Levittown
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I have had all kinds of issues with aftermarket IAC's, I've changed to a factory IAC and the Jeep runs like new, spend the extra couple bucks and get the right part.
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post #3 of 4 Old 02-01-2014, 08:59 PM
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1999 TJ Wrangler 
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Location: Minneapolis
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What codes are you getting from the CEL? I am assuming its on. If its not on that would surprise me.

1999 TJ
2000 XJ Cherokee
2010 Mustang
1964 Ford Fairlane 500
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post #4 of 4 Old 02-02-2014, 04:27 AM
Jonny Jeep
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1997 TJ Wrangler 
Join Date: Feb 2007
Location: Manchester
Posts: 5,812
Having to hold the accelerator down for a while to stop the engine dying could be an indication of a bad battery. If the battery is bad it could cause rough running and idle problems.
Get the battery charged up using a bench charger and then go and get it load tested.
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4.0 , low idle , no idle

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