Need help on Idle issue Maybe IAC problom

[pma4x4]

Hey, new to the forum. Longtime viewer first time posting.

I am looking at picking up a 96 Xj 4.0 auto A/C But one thing that has got me worried is its idle. Let me explain.

Starts and runs just fine. Has plenty of power and no noises. BUT, about ever 15 seconds almost clock work the idle jumps about 500rpms then goes back down. I thought maybe IAC so i pulled the IAC plug while runninga and the problem seemd to pretty much go away. It was running just a hint rough with the IAC unplugged but i plugged it back in and the problem came back.

There is no CEL but i am wondering if there is one in memory. Is there a paperclip way like some to jumper the connector or do i do the on/off/on/off/on trick like my 93 ZJ.

AM trying to diagnose this before the purchase.

I have also searched thru the forum and found many threads to the IAC but nothing with my symptoms

Any help would be great
THX

[XJING]

it might be the relay that sets the idle has one of its wires loose, or the IAC just needs cleaning. My money is on a very small vacumn leak somewhere though, just because of the small amount of rpm increase and it doesn't happen imediatley on start-up. The relay and the IAC would be affected if it happened on start-up since the rpm shift is later, check some of the vacumn plumbing. sorry so long winded. I can type faster than i can think sometimes.
Good Luck

[pma4x4]

but would a vacum leak cause it to jump like that like clock work? Like i said if i unplug the IAC the idle jumping goes away.

It does this 500 or so RPM jump right from a cold start and keep sdoing it even after warmed up.

[lawsoncl]

Was the a/c running?

[pma4x4]

It does it with the AC on or off. The AC needs a charge but the compressor still kicks on and off. Either way no matter what accessory is on or off it still does that idle jump.

I unplugged the IAC and the problem was almost gone. It would still change in idle but not as noticable or as much in rpms. plug the IAC in and it becomes more again.

[XJING]

Clean out the IAC, and be careful when you pull it out, I put a small clean rag under it so when pulling it out if anything falls out it doesn't get lost. Sounds like it just needs a good cleaning.( the little pintle gets dirty) Its not getting "set" to be your idle so its messing with the relay and thats why the RPM shift feels like clock work, the relay is trying to do its on off thing and the IAC cant put itself where it needs to be in its slot. So if you clean the IAC and it isn't your problem, go after the relay next.

[johnnyc]

When you remove the IAC, check the o-ring that goes between the IAC and the throttle body. I had an idle problem which was caused by a boogered up o-ring. Got a new one from the hardware store and all was good. Be very careful when installing the IAC back on. Make sure the o-ring seats properly in the throttle body.

[pma4x4]

Will check these later this week.

Where is the "relay for the IAC?

96 XJ 4.0 A/C

[tealcherokee]

Will check these later this week.

Where is the "relay for the IAC?

96 XJ 4.0 A/C

there is no relay for the IAC, but this is an obvious IAC issue, if you can unplug the IAC, and the jeep continues to run, its obviously stuck open. shut the jeep off, unplug it, and start it, it should NOT stay running, give it a good cleaning

[XJING]

I really thought the IAC is hooked to a relay. I will have to check the FSM. Well the concensous is to clean your IAC, the other thing with it being so slight in RPM's and it never hurts... is to retighten intake/exhaust manifold bolts. That can have an effect on small to large vacumn leak. Good Luck.

[pma4x4]

So do i just take off the IAC or do i take off that square housing it goes into as well. The square housing attaches to the main bod of the TB

If i do this do i need a new gasket for that housing to TB surface?

[pma4x4]

I swear I did not clean this up at all, it came outlooking like this.

AND YES I unplugged it then started it up and it stayed running. with the IAC IN but unplugged at the time. so do i take that square housin gthe IAC bolted up to off and clean that or what? should i try and see if it runs with the IAC completely removed??

http://www.arbrtek.net/images/temp/iac1.jpg

http://www.arbrtek.net/images/temp/iac2.jpg

[pma4x4]

ok.. Closer look has revealed that when the IAC is unplugged the engine dips slightly in RPMs every 15 seconds.

When IAC is plugged in and working it jumps UP about 500 RPMs every 15 seconds.

My guess is if its doing something either way every 15 seconds thne its not the IAC. I think the IAC is compinsating the idle to keep it from stalling.

I did the key onoffonoff deal and got no CEL codes.

Am thinking of just taking it to a dealer paying them the one hour shop time to diagnose the thing.

[lawsoncl]

That thing looks brand spanking new. I wonder if the previous owner changed it, trying to fix the problem?

[pma4x4]

same response i got from another forum.

I dont think its the IAC. i think something is causing the IAC to do this

[Blkxjkrawler]

this is kind of a shot in the dark here but when the a/c is on do the idle fluctuations coincide with the compressor clutch engagement? I have seen a/c systems with low charge have fast cycle times and the engine management adjust the idle speed accordingly. even stranger was that it carried over to when the a/c was off, recharged system and cleared the KAM (keep alive memory) and idle returned to normal.

[pma4x4]

KAM? clearing the ECU with battery disconnect? or something else?

Yeah AC is kinda low not nice and cold but cool. Will check that tomorrow

[pma4x4]

Your shot in the dark was a Bullseye!!!!!!!!

The temporary rev coinsides with the AC compressor shutting off. So the IAC cant adjust fast enough Hence the quick rev.

When the IAC is disconnected there was a small engine lag like ac coming on but it wasnt. when i plugged it back in it went the other way. yeah to the exact second its the Compressor.

OK now!! why or how does it carry over ot when the AC is not even being used or better yet how do i fix that.

You mentioned something about Kill Alive memory??? explain. I unplugged the compressor and left the battery unplugged for about 5 minutes and it still does it

Help please would like to take it to work tomorrow.

[Runnin'OnEmpty]

Ramjet, I'd erase the KAM as I described in the other thread (leave the door open), and here's another shot in the dark: Look in the relay center for the "latch relay", and swap it out with the A/C relay. If the trouble goes away, then replace the faulty relay.

The latch relay stays energized for a few seconds after engine shutdown, to set things up for the next restart. Including the IAC. This time delay stuff on the rolling idle makes me suspect the relay.....

[lawsoncl]

Your shot in the dark was a Bullseye!!!!!!!!

The temporary rev coinsides with the AC compressor shutting off.

Funny, I think I asked about the ac running earlier in this thread.

[Blkxjkrawler]

Glad I could be a service :) , And I apoligize in advance to all involved for being so long winded

Keep alive memory is basically the PCM's memory of the adaptive settings that it can adjust to suit your vehicles running conditions. Funny enough here I am on a jeep board giving advice on a jeep and I am not tottally 100% sure how to reset it on a jeep ( I have a scan tool that I can do it with but that is ford) you generally disconnect the battery for 5 to 10 minutes, and may have to leave a door open or such. BUT!!! if the root concern that origionally caused this behavior, ie A/C low w/ frequent cycle times is not repaired, you are going to be right back were you started very quickly if not immediatly.
I like the Idea of swapping relays as mentioned earlier. I would also charge the A/C, (come on, its june in AZ do you really need an excuse?) and then Clear KAM.
best of luck.

[pma4x4]

Ok Update.

1 battery was unplugged and door open for 8 hours. Still have the problem

2 My "relay center" does not house the A/C relay. The Powerdistribution center block under the hood does.

3 There is nothing that says "latch" either under the hodd, in my chilton manual or the owners manul that tells you what fuses and realys are what.

Any other name for this "latch relay"

pulled every fuse, and relay atteched to the A/C and it still does. it. I am running out of options and am almost ready to take it to the dealer. for the 1 hour diagnostics check. 85 bucks to say this part is bad. is almost worht saving on the headache. But i would rather fix it myself.

[pma4x4]

lawsoncl,

Quote:
Originally Posted by ramjet308
Your shot in the dark was a Bullseye!!!!!!!!

The temporary rev coinsides with the AC compressor shutting off.


Funny, I think I asked about the ac running earlier in this thread.

You did asked if it was running and i replied. but got no further reason as to the asking of the question. it revs no matter if the AC is on or off or the fact that u pull every plug, fues andrealy to kill the AC and it still does it.

All advice is being taken in this problem no ones idea is being turned down.

[lawsoncl]

You did asked if it was running and i replied. but got no further reason as to the asking of the question. it revs no matter if the AC is on or off or the fact that u pull every plug, fues andrealy to kill the AC and it still does it.

I asked about the a/c thinking it was probably just the compressor cycling, perhaps just as part of having the vents set on defrost vice actually turning the ac on. When you said it wasn't running, I figured I was off the mark and went back to lurking. I'm just as confused as you that the rpms are still erratic even with the a/c disabled.

[pma4x4]

I am thinking of just taking ti to a dealer here this week and have them figure it out

[pma4x4]

Well, cant get it to the dealer till tuesday morning. Also tried the TPS thats not it either.

anymore shots??

[XJING]

this is kind of a shot in the dark here but when the a/c is on do the idle fluctuations coincide with the compressor clutch engagement? I have seen a/c systems with low charge have fast cycle times and the engine management adjust the idle speed accordingly. even stranger was that it carried over to when the a/c was off, recharged system and cleared the KAM (keep alive memory) and idle returned to normal.

Looks like your ECM is still looking at your low charge on your A/C. As BLKxjkrawler points out. Get the system charged and then dump the KAM.

Quote by Runnin on Empty
The latch relay stays energized for a few seconds after engine shutdown, to set things up for the next restart. Including the IAC. This time delay stuff on the rolling idle makes me suspect the relay.....

I called this earlier in the post and was told the IAC doesn'a have a relay.
Thanks for clearing this up.

[pma4x4]

Will mention the low AC to the dealer. And they will be able to clear the KAM on the spot.

WIll pdate when i get back from Jeep on Tuesday

[pma4x4]

FIXED!!!

The used car lot I bought it from agreed to let me take it to a jeep dealer. I Took it there and only paying for a 1 hour diagnostics charge they found it 4 hours later to be the Computer itself.

It had seemed to go into a perminent limp mode/"i will run with the last thing i knew" type mode. One of wich was kicking the idle up for the AC.

Either way I pay 70 for the diag. hour and the dealer i got it from picked up the rest of the 470 dollar bill. and a genuine mopar ECU for 70 bucks!!!!

Case closed

Thanks to all for all the help, ideas and info. I now have a fully running 96 XJ Sport.