Idle Issues

Read a few other posts and already have an idea, but here's the story.

Information: 96 5.2L V8 with 143,000mi on it. 3.5"RE Lift. No engine codes. OBD II says engine runs slightly rich.

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Short story: Disconnecting IAC harness has no effect on RPM... good resistance across terminals as described in haynes manual. New IAC installed... no change. I can't figure this out, any suggestions?
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The LONG story: Four months ago it stalled out while braking to a stop at a light. Immediately restarted. Two days later it did it again... about the same distance from home, about the same operating temp. Eventually it stalled out one day (problem becoming more and more frequent) and wouldn't refire for about 10 minutes (after a few minutes it stalled again).

Taken to garage. Battery Temp Sensor replaced (free, because I told them before that it wasn't the problem), and, after stalling again, base idle adjusted. Vehicle ran well for a week, stalled again, and wouldn't restart for at least 10 minutes. Garage said they couldn't get any further with it and recommended the stealership, since they should be able to resolve a computer issue, should it have been the problem.

ZJ taken to dealership. Was called and told that they couldn't work on it. Went down there and was told that 'it may or may not be a computer issue, and we have no way of knowing what the problem is until we replace it, which will cost $500, and we can't guarantee it will work,' and then told me that they didn't want to do it without the OK because 'they had a heart and didn't want to rip me off' (BS). Aaaanyway...

I told them to work on it and tell me what they could find. Day later I get it back, along with an $81 bill and a service report that says 'unable to work on vehicle - been modified' and then says 'service manager says t-body binding.'

OK, so the throttle body is fouled up... I don't see it, but okay. Supposedly it was "Binding so bad we had to use a pry bay to open it." I don't get this at all, and if they had actually attacked my t-body with a pry bar I would've done the same thing to him. The convenient little problem is that Jeep no longer makes the t-body, so they couldn't help me.

Tried to order a salvage part from Quality Auto Parts (from uneedapart.com). They sent me a 1993 t-body which had a different and unusable throttle linkage. Ordered new one, specifying 1996 and they sent me another unusable one, both are awaiting return. In the mean time, having removed and thoroughly cleaned the original throttle body, I see absolutely nothing wrong with it and doubt I need to order a new one.

So along the way I realize that the Idle Air Control test procedure indicates a problem with the IAC. Disconnecting the wiring harness causes no change in idle (it used to). Replaced IAC twice and problem persists. Pretty sure the connection to the PCM is good as I get good resistance across terminals 1 to 3 and 2 to 4, both with key 'on' and the engine running. Also, doing the procedure throws a check engine light, so the PCM knows something is going on there.


Does anyone have ANY idea as to what I can do to resolve this? I'm lost and about to sell this car off and buy a hyundai (not really, but darn). Interesting note, removed the PCM the other day... on the back is written the VIN and vehicle information, along with 'TESTS GOOD, 134,960mi. 1/3/04.' So the PCM has been replaced, maybe that's the problem again? Thats my next move I'm afraid, not much I can think of left to do.

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I've seen it mentioned that battery should be discoed prior to installing components. Also mentioned possible CPS issue. Bought a new IAC yesterday but didn't disconnect battery prior to installing... this could be the problem. Never tried CPS, assuming that a failure there would throw a code, of which I have none. Any ideas?

If it were the CPS, I would think you would have more drastic failures, at least I did. Mine did not throw a code until it finally shut down altogether (after 2-3 days of internittent shutdowns) and I didn't get a look at the CE light code, I had my regular mechanic replace it. Frankly, now my 1996 has never been the same and I'm struggling as well.

Also, I think that the CPS is a hall-effect device which "should" shut you down at any point and not just when you are sitting and trying to idle.

Not sure if that helps much, but that was my experience with the CPS anyway. By the way, if you do change the CPS, I would get an expert opinion on which brands are best. Apparently, they can be pretty "iffy" with some brands and I am wondering if that has happend to me here...

Bryan

Ok you seem to be having on eof 2 problems. Either a bad Ignition Coil or a bad Fuel Pump.

I would start with the ignition coil, I guess to be sure next time it happens check for spark, I had the same thing happen to me last winter.
I was fucking around in a snow covered parking lot (donuts had engine tached at about 4500 rpms), well the jeep shutdown, after a few seconds it started up again, started to leave, did it again, pushed into another parking lot and waited about 5 minutes tried to start it and nothing, so I left it there till morning (knowing it had to be the ignition coil), the following day i went to get the jeep it started right up when I got there, had my bro in law go get another coil while I drove the jeep home, got home just fine and let it run for about 10 minutes it ran just fine. Well he got there with the new coil, I replaced it just to be sure. Then thinking my problem had been solved, I did some errands and came out from the store and the jeep wouldn't start, checked for spark and had no spark, well I was thinking maybe I got a bad coil from autozone, so I went to another part store and got a new coil, went back to the place where I left the jeep put the new coil on and it started just fine, drove crossed the parking lot and it stalled, so I had my bro in law tow me home. where I inspected everything, got the jeep to started up again, checked all the wiring to make sure there wasn't a loose connection and while inspecting the plug wires I got zapped. There was a bad plug wire, that I knew about (replaced manifold gaskets a few weeks before all of this and for got to put heat shield on and the wire touched the manifold and burnt through it), so I replced the plug wires and haven't had the problem since.

What was happening is the bare plug wire was arcing real bad which caused the Ignition Coil to overheat and shutdown and this is why it always took a few minutes for it to restart again.

This also occur with the fuel pump it will overheat and shutdown, mostly when it is below 1/2 tank, which is when the [ump if no longer fully sybmerged in fuel.

like I said, to be sure this is your problem, next time it happen, check for spark. if you do not have any spark then the ignition coil is the culprit. Replace it and check the plug wires for damage or carbon tracking on the inside (carbon tracking also causes arcing which will overheat the coil), heck if you haven't changed them in awhile nows a good time.

Know it isn't the coil, as that was replaced <6mo. ago and was checked for spark as soon as the incident first happened... plus the last time my coil went bad it would cause stall through all driving ranges.

Fuel pump... I wouldn't think so. Friend with a 98 5.2L had his go a fe wmonths back and it was a totally different set of symptoms, mainly loss of power at highway speeds, followed by stalls. My issues only occur at low idle braking to a stop or stopped. Did a search on idle air control in this forum and about 10 other people have had the EXACT same problem. But no real solution is reached in alot of threads... just 'replace the IAC.'

Did an interesting experiment last night... since I have about 3 or 4 IAC's around, I left the new one in the throttle body, disconnected the wiring harness, turned the engine on (running) and plugged an IACV into th eharness. The needle slowly extended to full (in very jerky pop-pop-pop fashion, not smooth, don't know if it should be). Apparently the car knows that the IAC is there - check engine when crossing terminals with multimeter - it controls the IACV... it just can't idle properly.

Maybe it is the throttle body. I've got one on ebay thats ending in 3 or 4 days. Maybe that will fix it.

well if it only does it while slowing down for a stop (when you are not pressing the gas pedal) then the IAC would be your problem. Did you disconnect the battery when you replaced the IAC. The only part of the throttle body that would cause this would be a dirty passage way for the IAC valve. Clean the Passage way with some TB Cleaner and replace the IAC (remembering to disconnect the battery).

T-Body removed and cleaned with a wire brush and carb cleaner. I did NOT disconnect the battery when replacing IAC, but I've replaced it in the past (anytime you unplug the harness to check function it's as if you're replacing the IAC) and I never had a problem with it. If every sign wasnt pointing to the IAC then by now I'd be REALLY sure that it wasn't the IAC... guess I'll try one last IAC with a disco-ed batt and see what happens.

Update... new CPS, checked and reattached all spark plug wires (after thinking they were attached wrong as per chilton book... turns out it wouldnt start routed like that).

Now jeep runs... but disconnecting IACV does nothing to idle... STILL. Doesn't stall at low idle, now stalls just driving down the street at speed. WTF?? ANY ideas here?

And yet it runs if you just sit there in the driveway?

Sometimes runs while parked, sometimes not...

Update: Replaced O2 sensor. Ran fine for a week, but didn't trust it so it never left the neighborhood except for once to get gas. Took it for it's daily test drive tonight and she stalled, first at low idle, later (after managing to get it turned over about 15 min later) at 2000rpm in neutral at a stopsign trying to limp home.

I'm totally lost on this one. Changing CPS caused a different type of stall, and O2 seemed to fix it, but it still does it. My next step is to pull the intake and see if I can find a leaking intake manifold gasket or plenum pan gasket.

Any other ideas?