NickDog

Hey there CF!

1999 Cherokee Classic 4.0, 4x4, Automatic

I have searched numerous threads and figured it was time to post up before I proceed with a chainsaw or find a jeep wiring god in the region.

I am tracking down what I think are electrical gremlins--I am experiencing a high idle. The Jeep will drive itself up to 30. It's like cruise control, but undesired.

Not sure if its related, but I am also experiencing intermittent gauge cluster non-functioning issues, sometimes the whole cluster is affected, at other times just the speedo and the tach. But then I hit a bump and its all fine and working again. Thought about swapping the Vehicle Speed Sensor on that score, but not I am tapped out for a bit. The connection looks ok though.

Also, my entire exhuast from the head/block back (kept the cat) has just been replaced, as well as a new intake manifold. No vacuum leacks. New throttle body gasket. "New" JY throttle body, New TPS, New IAC. New NGK o2s. New Coolant Sensor.

But my "IAC issue" continues...

Latest trouble codes are p0505, p0123,0122.

After swapping parts in and out, I think I am dealing with an electrical rather than mechanical issue.

Yesterday, I got an entire sensor/throttle body setup off a wrecked 98 sport and did a direct swap, just to see what would happen. Unless I hit the gas, however, the Jeep did not want to start, even after resetting the computer to learn mode.

I revved it up a couple times, put in gear, and got it to maintain a low idle, about 250-400 RPMS. I took it and drove it and it rocked and rolled at speed, but back to 250-400 rpms at stop. Sometimes, at occasional stops, when corning in a parking lot slowly, or stopped going up a hill, it would die. Elsewise, she dominated. I was hopeful for sure.

However, this morning, I went to start and I couldn't get her to hold an idle. So I cleaned the used-but-new-to-me throttle body and put in the sensors from my old throttle body. Back to high idle.

D**n! I was so fleepping close!

With everything plugged back in I left the IAC out of the housing. Had my helper turn the key to see if the IAC moved or shook. Nothing on the mopar part or the Autozone (standard part) I had lying around. This led me to conclude that the wiring was at issue.

I checked for continuity from the IAC connector to the unplugged PCM connector end of the harness and had continuity between each point (0.00). However, when I check continuity from the IAC wiring harness to ground (negative battery terminal) I get 102 ohms on female slots 1 and 3, and continuity (0.000) on 2 and 4.

My understanding here is that there is a short, then, on wires 2 and 4? (Man I freaking hope so!) Or am I reading this backwards?

I inspected the untaped portions of the wiring harness near the firewall and saw a few trouble spots on three wires--some chaffing and exposted wire--two of which matched the IAC wires (same colors).

I put e-tape around them for the moment to prevent them from rubbing on anything but it doesn't alter the readings on my multimeter after the fact. Same readings and idle.

Flip.

At this point, my thoughts are that I should splice new wires from the IAC connecter end to the PCM connector end of the harness.

My only issue is that one of the wires (grey with red line) on the PCM end, has some chaffing/wear/exposed wire on it, right where it enters the connector. Even if I bring new wire just short of that point, I am wondering if that chaffing will cause problems (because it might already be doing so?)

Sorry for this long-a post. I hope it helps others in some way. This has been literally months in the troubleshooting and a total PIA.

I thought about splicing in all 4 wires just to be safe. I guess I could check the TPS wires for continuity to the PCM as well.

Either way, I wanted to get some feedback on this issue before I go John Wayne on this thing and kill my daily driver by accident, which would suck enormously.

Let me know what you think, CF!

Thanks for chiming in! Cheers!

NickDog

Well, I went ahead and spliced and soldered all new wires from the iac to the pcm. I will wait and see if my idle gets unstuck over the next few weeks, but I am not keeping my hopes high. The idle is still seemingly stuck, but acceleration is very smooth.

Here's to hoping the pcm will adjust and fix the problem...

DFlintstone

Man we feel for you! Btw, powering up an IAC that is out can ruin it. Says that in the FSM, you need to stop before it goes out too far. I had this "canned" maybe might help>>

Vacuum leaks suck. I go around with short little shots of starting fluid, if you hit one the sound of the engine will change. Small little shots! You don't want that stuff to accumulate. It's a fire hazard, but It evaporates right away. Also with a tube, or a section of hose you can listen for it. Don't forget the lower O rings on the injectors need to seal as well. (uppers would leak fuel).
The manifold bolts have a habit of loosening, especially that rear one. On anything like that you never want to tighten only one. It can warp/bend, even crack things. If I found that any that where easy to reach where loose, I'd pull the air cleaner and tighten them all, starting in the middle and working out towards the ends. I go over about three times. It's a bear of a spot to get a torque wrench on them all. Just don't ape on it. If its firm and not turning, no point in going on to break it, a REAL *****. The rearmost bolt underneath takes a little doing, but it can be done with the right extension. For that very back one by the firewall I use way long extensions (18"), with a swivel at the socket. Anyway, that's a good thing to check on any old Jeep. ALSO, there is a large line coming off the intake, rear of the TB that goes back to the firewall, across, then forward down to the vacuum ball behind your right front bumper. You can pinch that off or unplug it and cap the nipple to test if you have a leak there. The line to the break Booster can also leak vacuum.

NickDog

Thanks DFlintstone for the direction.

Now I am wondering if the IAC is bad and was bad to begin with?

I bought it from WeRMopar.com and it shipped in a large flat rate box in which the IAC was left, unbelievably, to bounce around, which could have f'd up the pintel. Whoever packed it was a jackwagon. But the onus is on me, since I am the one who dragged my feet on filing a return and missed their return window.

I do hear the computer trying to bring down the idle (or what I think is the computer) at speed. I am wondering if I should take my shot with another, new IAC.

It could be other issues, but I have only so much time to diagnose and jack with it.