Novak Conversions Jeep Wrangler TJ engine mounts

Chasing a high idle, should the IAC be adjustable?

GregBelleville

TJ Addict
Original poster
Supporting Member
Joined
Sep 19, 2022
Messages
1,016
Location
Southern California
Hey everyone, I'm chasing a slightly high idle on my 99 4.0 TJ with the 32rh.

The engine idles right about 1000 rpm when in park, and when I tried to take my jeep in for smog today the tech wouldn't even test the Jeep, he could hear the high idle and told me that alone would cause it to fail, so he sent me on my way.

Things I've already tried:

  1. Clean throttle body (both while running by spraying carb cleaner into it and also pulled off the Jeep and cleaned on the bench)
  2. Checked for vacuum leaks -i did a diy smoke test through a port on the intake manifold and could not find a leak anywhere. I've also tried spraying the vac lines with throttle body cleaner with no luck either.
  3. Throttle position sensor was replaced with a new Mopar about a year ago
That brings me to today. I'm suspicious of my IAC so I pulled the throttle body off the Jeep and removed the IAC. I recleaned the IAC port and the IAC housing.

One question I have though is whether I should be able to adjust the length of the IAC tip in and out because I can't seem to adjust mine at all. I've seen videos where you could pull back the collar and rotate the tip in and out to shorten or lengthen it. When I try this on mine I can't get it to spin at all? I read that the tip should be out about 1⅛" and mine is about ¾" so I tried to adjust it and ran into this problem.

Does this seem faulty that I can't get it to adjust at all?
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If you can't move it at all i think that's an issue. But try this: put it all back together but leave the IAC itself out of the housing but still plugged in. Have a buddy start the car. You should see the plunger extend as the computer will think it's getting too much air. That will tell you if it's seized or whatever.
 
If you can't move it at all i think that's an issue. But try this: put it all back together but leave the IAC itself out of the housing but still plugged in. Have a buddy start the car. You should see the plunger extend as the computer will think it's getting too much air. That will tell you if it's seized or whatever.

Well after cleaning it back up and reinstalling it (before I saw your message) I fired her up and wouldn't you know it, idle drops down to around 760 RPM.

My suspicion is that the small gasket for the IAC was positioned the wrong way,I noticed when I was cleaning everything that there was an area on the gasket that was a little dirty where it is supposed to be covering the housing surface I circled below. It is not easy to tell when the gasket is positioned backwards unless you really look closely because all of the screw holes still line up. The dust I found on that one area of the gasket makes me think it wasn't on correctly.

When I started her up she initially started out around a 1000 rpm as usual, but within maybe 30 seconds she gradually lowered down into the 760 range which makes me think the IAC is still functional and making the adjustments it should?

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760rpm sounds way better. I think I idle around 650ish, so you may still have something breathing a little extra, although I don't know what the error bars are on "average idle speed" whatever that number actually is.
 
760rpm sounds way better. I think I idle around 650ish, so you may still have something breathing a little extra, although I don't know what the error bars are on "average idle speed" whatever that number actually is.

They told me I had to get it under 900 at a minimum, so I'm planning to take it back tomorrow and see if she'll pass now.
 
Novak Conversions Jeep Wrangler TJ engine mounts