I dont think it's your AIC,sounds like you have a serious vaccum leak bypassing the AIC...or..make sure the AIC is for the 4.0,....the 4.0 and 2.5 AIC's look the same and are interchangable but are actualy different,i know when doing a 4.0 throttle body upgrade on a 2.5 you have to use the 2.5 AIC or it will idle through the roof also

 

Thanks for the reply. From everything I've read, it's the IAC. I don't have a vacuum leak, I've checked every line.

Even if it is something else, I still have to get the IAC set correctly to reinstall it. I bought a new IAC and MAP sensor and I'm going to swap them out tomorrow.

If it's not that, I'm stumped.

 

lol..i just noticed i got IAC backackwards(AIC)...anyways......i never knew there was an adjustment on them,but i'm not a real tech expert on them either.
Since you said you just done an engine swap,just a few things come to my mind,,intake manifold gasket leaking,throttle body gasket leak..cracked intake manifold or throttle body, etc.Just some things to look at other than vaccuum lines for leaks

 

lol..i just noticed i got IAC backackwards(AIC)...

No problem. I am civilized enough not to mention it, but I laughed a little too!

I'm fairly sure that I don't have a leak anywhere. I've checked! But, I can look again. I still think it's the IAC or the MAP. I'm going to replace them both and tinker with it when I have more time this weekend.

Good information though! I sure do appreciate it.

 

How long did you let it run? How high a RPM? I did a 4.0 TB change on my 2.5 and it ran a high idle for about 45 seconds and then the computer brought it down to normal...

 

I don't recall seeing (or ever using) an adjustment screw on the IAC. There is a screw on the throttle body that's factory adjusted and not recommended for re-adjustment - here's a quote from a FSM:

"A (factory adjusted) set screw is used to mechanically
limit the position of the throttle body throttle
plate. Never attempt to adjust the engine idle
speed using this screw. All idle speed functions are
controlled by the PCM."

If you think it's the IAC, why not "bottow" a know-good one from someone for a test. It does sound like a vacuum leak - I'd be looking for a gasket leak. Have you had the throttle body or intake manifold off recently?

In my experience, MAP sensors don't often fail, and when they do, the engine runs very poorly.

 

Assuming you have the correct IAC for the engine and i'm not tryin to be a wise guy but is it on correctly? I had one i thought was bad on a mustang so i took it off and put the new one on and had the same problems. I finally figured out i had it on backwards and i felt pretty stupid after i did it but it was 180 degrees out and i'm assuming the jeep iac can be put on the same way. If it's on correct try resetting the computer and see what happens next. I've never seen an adjustment on one before though.

 

Still having problems with it. Not sure what the problem is!

Alfons, there isn't an actual "set screw" for the adjustment. The piston/plunger is threaded so you can adjust it in or out. It can be adjusted. I thought it could be the MAP, because it's running like crap! But, I swapped in a new one and it didn't make a difference.

Griggs, I don't think it would make a difference if the IAC was 180 off. The IAC just opens and closes by moving a piston in and out. Either way it was installed, it would do the same thing. It's installed the way the old one was originally installed.

Dos0711, I didn't let it run that long. The idle was instantly so high, I was afraid I was going to have engine damage so I shut it down. I know the PCM needs to adjust it, but it's crazy high!

I'm stuck. I have no idea what to do at this point.

 

you can not "tune" the IAC to a specified potion as the ECM will open/close it to its set value based upon that Temp. Also they make two different IAC valves, one that requires power all the time....this one will free spin. Than the other will require power to move the needle in or out... this one you cannot turn by hand.

It is possible that the one you bought is defective. I have worked at Advance Auto and you would be amazed at how many NEW alternators and starters that would test bad.

With this said you can do a simple test to ensure the needle is moving. Take the IAC out and leave it plugged into the harness. Have someone Key the ignition and you should see/feel the needle close/open. If it does not you may have a bad IAC, or it could be a computer issue.

 

i have and fixed the problem

i had the same problem but i rebuilt my engine with new seals rings and everything you can think of. then i started it up and it did exactly what yours does.

so i took the iac out and screwed it out( to decreases air flow) (makes it longer)

one turn at a time then put it back in( with one screw ) to make it easier to take back out.

i did this till it was just right. not only does this affect idle but it affect accelerating air that the engine takes in. so it decreases (bogging) if you get it just right.

i now run perfect idel and everything.

after you get it all set and perfect: reset your computer

STEPS:
unplug pos+ terminal and touch to neg- for 3 sec
then put pos+ terminal back on
turn car to on but DO NOT START
then turn lights on
then turn lights off
then turn car off and take key out for a few mins.

a guy showed me all these things and thought them step to step to me.
this is a guy who goes to college to work on jeeps that he loves.
so he has to know what he is doing. (I think)

i suggest to watch some videos on how to turn the iac in and out. its hard to explain. you hold down the tube around the tip
then turn the tip, the tube is spring loaded. and DO not turn the tip to far out that it will fall out haha.
i will upload a video on how to do this if you want.

**remember everything and anything say is not 100% professional statement. so be safe make the right choice and if you have any doubt that you can not do it right. DON'T DO IT AT ALL!**

 

"A (factory adjusted) set screw is used to mechanically
limit the position of the throttle body throttle
plate. Never attempt to adjust the engine idle
speed using this screw. All idle speed functions are
controlled by the PCM."

I did this on the 4.3. so far no problems. They mean this! There was a tin cap covering the screw that I had to remove first

 

Mine was the intake gasket. The exhaust manifold is different thickness as the intake manifold.

 

Welcome to the forum. You should step over here and provide details of your jeep. Which incidentally: what is your jeep? Because aren’t all the YJ iterations a single gasket?