I installed a 60mm jeep TB with my new motor a few months ago. Ever since then I have had nothing but problems with the car idling. Its almost like the IAC has no idea how to control the idle anymore. It use to not be that bad, maybe idling around 1500rpms and surging alot when rolling in neutral. It ran this bad on the stock ECU. Now Im running MSnS and it seems to have gotten worse. Sometimes the car will idle ok and others it will hang up at 2500rpms and just stay there. I will push the TB plate closed with my hand to make sure its closing and it doesnt help at all. I have tried 2 different IAC motors and both do the same thing? Any ideas? When the AC is on sometimes the car will idle around 900rpms and sometimes it wont make a difference. I have had to turn the car off before to get the idle down from 2500rpms. Im about ready to throw this damn TB in the trash.

It takes alot of work.

Did you push the IAC tip all the way in, then reset the ecu? It will start at 3.5kish then work its way down to 1k or below.

Thats how I set the Jeep TB's.

Stupid question I know, but did you adjust your throttle cable as well?

Also, if the TB spring is TOO tight as in pushes against the TB and throttle cam, you will hang at certain RPMs.

If I screw the IAC all the way in it will only stick out like 1/2 inch. I unscrewed the IAC tip to about an inch and left it at that. I didn't reset the ECU when I put it in but it has been done several times working with MS. The throttle cable has a tiny bit of slack so thats not the problem. Also the spring is pretty lose. I had to put a small bungey cord on the throttle to make sure it holds the plate closed good.


I removed the 57mm lip inside the TB before installing it. I tried not to grind any part where the plate sealed but if I did nick it a tiny bit would that cause the idle to be high? Like if it was letting some air by, but then I would think that the ECU would see the idle is to high and close the IAC some. Maybe I will try to screw the tip in all of the way and reset the ECU to see if it fixes the problem.

tim, i hope i don't have all these damn problems w/ mine... :thumbsdown

Ok I just went and tried what you said. I screwed the IAC motor in all the way and reset the ECU. The car idled down pretty quick but idled around 1200rpms which isin't to bad. Took it for a spin and it drive about the same. It will idle around 2k when rolling in neutral and surge some. When still I can rev the car up once and it will drop down to 1200-1500 but it I tap the gas 2 or 3 times the idle hangs up over 2k. The throttle plate is closing all the way so its got to be the damn IAC motor.

I looked for leaks around the TB and found no big ones at least. I unpluged the IAC and hooked up a spare I had to see whats going on with it. When I tap the throttle the IAC motor opens also which was weird and sometimes it will stay open for a few secs which would explain the idle hanging up. I still have the TPS and CAS sliced into MS and also running to the stock ECU. Should I just run these to MS and maybe that will help out with the IAC motor freaking out some?

The idle still has never come back down to 900rpms unless I turn the AC on. Is the IAC chamber to big allowing to much air to enter the manifold to idle that low not under load?

You shouldnt Mikey.

At first maybe, it took me a few days to get it right. But I let my car idle for 10 minutes before I took yours off the car Mikey.

The idle hanging at 1500-2k while in neutral is normal from what I have read. If you pay attention, your stock TB will do the same, only around 1200. The 60mm makes the problem more apparent.


Did you swap the tip out for the Jeep one right? Check all your gaskets. Make sure the TB is flush against the IM.

Yes I switched the tips with the jeep IAC motor. My stock TB idle perfectly at 850rpms every time and when rolling it would stay at 1200rpms. I never had a problem with idle surge when just sitting still. Im going to swap back to a stock one to see if the problem is being caused by the TB to begin with.

I blocked off the stock IAC hole with a bolt and cut half the head off so the Jeep TB would sit flush. And put gasket sealer on the gasket before installing it so I shouldn't have any leaks. I may take it off and check for gaps around the flapper. Fix any of those if I find some and it that doesn't work Im blocking off the IAC and using the throttle plate to control idle.


This is just an idea, but since this TB is off a 6cylinder which requires more air at idle. The IAC passage is allowing to much air to come in making the car idle high and the IAC cant restrict enough air? What if I took the IAC chamber off the TB and someone make the chamber small so that less air could flow through there.