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Old 09-15-2008, 11:29 PM   #1
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Jeep won't idle after Battery went dead.

Hello, the lights on my 1999 Wrangler TJ were left on and the Battery went dead. I jumped it and now it won't idle. Is this the Computer, it ran fine before the Battery went dead. Would disconnecting the Battery for a while reset the Computer? Any thoughts?

Thanks.

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Old 09-15-2008, 11:47 PM   #2
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your fine, it just has to learn to idle again.bring the rpms up for a while just enough so the motor doesnt die and it will re learn in no time.

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Old 09-15-2008, 11:49 PM   #3
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Thanks, I'll try that.
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Old 09-16-2008, 12:01 AM   #4
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i do not quite understand how it learns it seems like it should have a pre-set deal but everybody claims it learns so majority rules
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Old 09-16-2008, 12:12 AM   #5
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When you disconnect a battery you are doing like a hard restart of a computer. It will reset - Then when the computer turns back on it comes up with would you like to restore from a old point. The trucks computer does the same thing. The PCM will reboot and will run in like 5 to 10 mins perfectly again assuming your battery is not shot ie not holding a charge then this will keep happening.
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Old 09-16-2008, 12:14 AM   #6
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Thanks, I'm going to try the Computer Reset and replace the Battery if necessary.
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Old 09-16-2008, 08:24 AM   #7
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Disconnect it, let it sit for a half hour or so, reconnect it, start it up and take it for a drive, hiway is preferred, this seems to be the best method, reconnecting it and starting it then letting it idle for a while has caused me some strange problems including a 'dead' spot in the throttle position sensor that went away when I did the hiway thing.
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Old 09-16-2008, 09:36 AM   #8
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You can take the hot cable off and hold it to the negative post for 30 seconds to reset the computer.It is quicker than letting it stay off for 30 mins or more.The computer has a capacitor charge that will be drained within 30 seconds by grounding out the hot cable ONCE IT IS OFF.After you hook the positive cable back up they also recommend turning the ignition switch to the on position without the engine running then turn on the headlights and then headlights back off then turn the key off.Then hop in and start and take a drive above 30MPH.Also the computer has a preset set of codes it goes by once started and then once it gets up to normal operating temps it will start reading all the sensors and start the learn process and reprogram the standards for which it runs best.
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Old 09-16-2008, 10:37 AM   #9
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Your idle problem is strictly related to the fact your battery is dead. Nothing else. The alternator requires voltage from the battery to work (called an exciter voltage) and when the battery is too dead to provide it, the ignition system doesn't get enough power from the alternator (or none) so the engine will not run or idle once the jump battery is disconnected.

Give the battery a good deep overnight charge or replace it and your idle problem will be fixed. Guaranteed.

Our Jeeps use a common kind of alternator that cannot put power out unless they get that exciter voltage from the battery. No battery? No alternator output and the engine will not run. Only a few alternators don't require a battery to work. It was the old generators our cars used to use where it would still run and the generator would put out power without the battery being in place.
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Old 09-16-2008, 11:02 AM   #10
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I had stalling problems after my wife killed my yellow top by leaving the lights on.

I put it on the charger over night then did a load test on it. the battery was 100 percent charged and I still had stalling issies until i drove it a few miles.
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Old 09-16-2008, 11:10 AM   #11
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Quote:
Originally Posted by Rawkon View Post
I had stalling problems after my wife killed my yellow top by leaving the lights on.

I put it on the charger over night then did a load test on it. the battery was 100 percent charged and I still had stalling issies until i drove it a few miles.
Two different issues. It wouldn't have idled at all if the battery was dead after removing the jumper cables. Then after the battery was fully charged, the engine can idle roughly because the computer sometimes, depending on how dead the battery was and yours was completely dead, has to relearn its parameters.
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Old 11-18-2008, 05:26 PM   #12
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Quick question, I removed my battery to try it out on my Cherokee and when I put it back in the TJ, it starts and immediately dies again. I already planned on buying a new battery but is this because I need to get my rpms up and drive?

Thanks
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Old 11-18-2008, 11:10 PM   #13
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Quote:
Originally Posted by statler392 View Post
Quick question, I removed my battery to try it out on my Cherokee and when I put it back in the TJ, it starts and immediately dies again. I already planned on buying a new battery but is this because I need to get my rpms up and drive?

Thanks
The simple answer, yes, they all run like crap for the first 30 minutes or so. One of the Chrysler techs said a trick is to start it up and hold the throttle at 3,000rpms for 2 minutes. I might try that is it was warmed up but not with a cold engine. It's just as easy for me to drive it.
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Old 11-19-2008, 12:04 AM   #14
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Well, I guess I have some driving to do...

Thanks man
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Old 11-19-2008, 04:11 AM   #15
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Its happened to me also . I got freaked,thought I did some crazy damage.After a short drive it was fine.

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