new iac causes high idle

[tupeloranger4x4]

my truck had problems when it was hot that it would idle rough and make a horn sound.found on the 4.0 forum that it was most likely the iac.i bought and installed the new one this morning and it causes the truck to idle high at initial start up(2k)then barely slows up to about 1500.is the iac not my problem?

 

[Big Jim M]

Sounds like maybe you have created a vac leak when you did the install!!
Big JIm

 

[tupeloranger4x4]

i put the old one back on after and its fine.so would the new one be defective somehow?

 

[Big Jim M]

Yep!
Big JIm

 

[tupeloranger4x4]

swapped new iac with another one and it does the same thing.

 

[Nhaz]

You may have more then just a IAC problem. It could be combined with a vac leak somewhere.

 

[Big Jim M]

Same brand? Take it back and go to another parts house for a different one. If it's also bad then look to your install.. A small vac leak will cause what you are posting.
Big JIm

 

[tupeloranger4x4]

yea i just tryed a third from a different place bt same brand.when i unplugged the iac as its stuck at high idle it then idles where it should.i noticed that on the back of all the new ones it has a slight different shape in the ports so im thinkin that the gasket maybe isnt doin its job and causin a leak.im searchin for a new brand to try tomorrow after work

 

[Earl43P]

It does sound like you may have a vacuum leak.

IAC should have come with a new gasket, but they are small enough to cut a gasket to fit if you can't find one. I toyed around with different sized holes in that gasket, trying to cure the hung idle until you stop (normal - but I've never liked it).

You know, it could also need to relearn its idle after compensating for a bad IAC for however long. Try resetting the computer with a new IAC installed (I think all of the ones you bought were in fact "good").

Simply disconnect the battery, turn on/off the headlamps, reconnect the battery and start it. Set the PB, let it idle in Park or neutral (stick) for 5 min. Then turn on the AC let it idle for 5 min.

Then put it Drive, idle 5 min then drive with ac on for another 5, then drive it.

 

[kimcrwbr1]

+1 on resetting the computer with a good seal where the IAC merries up to the TB on my jeep the O-ring didnt seal and the IAC plunger pushed all the way out of the housing trying to lower the idle.

 

[tupeloranger4x4]

earl43.i do agree that there was nothin wrong with any of the new ones but i think it is some sort of installation error.i unhooked the negative terminal to reset the computer however i didnt give it time to adjust like you suggested.when i get time tomorrow to try it again ill let yall kno.also it has been running with a bad iac valve for about 6 months now