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Unread 05-29-2014, 10:06 PM   #1
bradleyheathhays
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1996 XJ Cherokee 
 
Join Date: Mar 2008
Location: Lexington, KY
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Left lights on w/ batt drain then motor won't idle on restart

'96 XJ here and I forgot and left my headlights on, so 45 mins later everythings totally dead at key turn. No interior lights, nothing.

Get a jump and the 4.0 only starts when I give it a little gas. Had to two foot it for a while b/c the motor would die if I wasn't giving it at least a little gas. After reaching around 50 mph the motor seemed to be ok and I could single foot it again at stop signs etc.

Next day start it up and back out and it dies again. So same thing, tendency to die at stop signs unless foot on the gas. So I get up to around 50 again and it starts to act normal again.

So what's happening here? Did the batt drain reset the computer or something and now it's learning how to idle again? Is there anything I can do to help it learn faster?

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Unread 05-29-2014, 10:59 PM   #2
M35A2
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Most likely the puter reset. If i let my bat die, it does the same thing for a day or so.
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Unread 05-30-2014, 05:07 AM   #3
JMH21814
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That doesn't sound quite right. Yes, the PCM probably lost its adaptations, but a relearn is usually pretty quick. The idle would go way up, then way down, then settle somewhere in between for the IAC. Sounds to me like your IAC is stuck in a barely open position. Won't idle cold because it needs more air, will idle once it warms a bit because it needs less air.

I've never had luck cleaning IACs, others have. You could try cleaning it or replacing it, but before you do, verify power and ground with a DVOM. Good luck.
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Unread 05-30-2014, 05:50 AM   #4
Mwildmann
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I don't have an explanation but mine did the same thing to me last fall due to a dead battery. Got it jumped, but it would not run without a little throttle input. After sitting there for 15 minutes or so with the rpm up a little, it would maintain an idle. Could it be that the battery was consuming too much amperage during initial charging from the alternator and there wasn't enough juice available to run the engine? Sounds goofy, I know but it's all I can come up with. I replaced my battery and all has been good.
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Unread 05-30-2014, 08:38 AM   #5
Tru2Chevy
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The computers we have are very picky about getting proper voltage, so once the battery has been killed they will have to go through a relearn, but that should only take a few minutes.

Are your voltages still good since the jump start? Any slowness in cranking speed when you start it up? If so, it's possible that you killed a cell in the battery. I did that a few years ago on my '96 and chased issues like this for a few days before I went and had the battery tested.

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Unread 05-30-2014, 09:09 AM   #6
chris87xj
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x3 or 4 or whatever on checking out that battery. Full discharge is hard on them and can push a borderline one over the edge.
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Unread 05-30-2014, 04:09 PM   #7
Kevin108
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When the battery dies, the computer freaks out. Give it some throttle and keep it alive. Powerbrake and take it around the block and it's usually back to normal after that. I've gone through this at least a half-dozen times on my last battery. The Optima I have in there now just starts like normal if I leave the interior lights on all night.
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Unread 05-31-2014, 08:27 AM   #8
um7267
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Quote:
Originally Posted by JMH21814 View Post
That doesn't sound quite right. Yes, the PCM probably lost its adaptations, but a relearn is usually pretty quick. The idle would go way up, then way down, then settle somewhere in between for the IAC. Sounds to me like your IAC is stuck in a barely open position. Won't idle cold because it needs more air, will idle once it warms a bit because it needs less air.

I've never had luck cleaning IACs, others have. You could try cleaning it or replacing it, but before you do, verify power and ground with a DVOM. Good luck.
the relearn can take some time, start it up and idle it at 2000rpms for 5-10 minutes it should stay on after, i had that issue with my last jeep
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Unread 05-31-2014, 08:58 AM   #9
JMH21814
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Quote:
Originally Posted by um7267 View Post

the relearn can take some time, start it up and idle it at 2000rpms for 5-10 minutes it should stay on after, i had that issue with my last jeep
Fair enough. In my experience, though, after replacing an IAC or clearing adapts in most vehicles (including jeeps) it runs on its on its own without having to feather the throttle. The only vehicle I can think of off the top of my head is the nissan maxima. That idle relearn is a *****.

But I certainly don't know everything and am willing to admit when I'm wrong. I hope the OP keeps us informed of what the solution is. I am eager to know.
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