TJ starts but won't idle, then dies

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Rick2004LJ

TJ Enthusiast
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Jun 11, 2018
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Texas
Sorry if been covered but wasn't able to find my problem in a search.
2004 LJ 4.0 Auto 125K Miles - Just recently began having a starting problem. Engine cranks and starts quickly but wont idle and immediately dies. If I hold a little throttle it will rev but the minute I let off it immediately dies. Only happens occasionally but always when it has sat overnight.

First time it happened I disconnected the battery for a couple days - reconnected battery and started just fine. Just happened again and dont know what to do. Live in Houston so no cold weather issues.

Any ideas appreciated. I can turn wrenches but not very experienced with starting/fuel system issues. TIA
 
Jerry Bransford said:
A TJ engine won't stay running for Long with a dead or nearly dead battery. Have you had to jump start your Jeep lately?
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No Battery Issues I know of. It cranks good and starts quick - just wont keep going....
Will check battery just in case - start with the simplest solution first Right?

Thanks
 
If your battery is good, idle issues are commonly caused by a dirty IAC (idle air control). The IAC is what provides all of the engine's air at idle rpms and if dirty/clogged will cause idle issues.

Spraying an aerosol throttle body cleaner into the throttle body while the engine is running at idle RPM's normally restores it to good operating condition. Don't raise the engine rpms above idle rpms while spraying the cleaner into the throttle body or the cleaner will bypass the IAC and not clean it. The cleaner will flood the IAC and cause the engine to stalk. That's OK and actually good since it gives the throttle body cleaner more time to work. Just restart the engine and do it again. I try to get at least 1/3 of the can of cleaner through the IAC.
 
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Always start with the simplest solution, which in this case means having the battery load tested. Also, test the alternator just to be sure as well.

After that, I might suggest cleaning the IAC and throttle body, as that is known to cause idle issues, and is very, very easy to clean / rule out. See this thread: How to clean your IAC (Idle Air Controller) valve
 
Having the same problem with my Wrangler..Left the key on all night..was checking something and just left it on. Went out this morning and nothing. Charged the battery for an hour or so..Jeep started but died as soon as I took my foot off the pedal.again again again..I have the battery on charge again. Might as well right? Im going nowhere now. My son is bringing me some throttle cleaner so well see..This Jeep along with my Cherokee is killing my wallet! Mabe ill buy a Chevy? LOL
 
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bigwheel53 said:
Having the same problem with my Wrangler..Left the key on all night..was checking something and just left it on. Went out this morning and nothing. Charged the battery for an hour or so..Jeep started but died as soon as I took my foot off the pedal.again again again..I have the battery on charge again. Might as well right? Im going nowhere now. My son is bringing me some throttle cleaner so well see..This Jeep along with my Cherokee is killing my wallet! Mabe ill buy a Chevy? LOL
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A hour or so is not long enough to charge the battery, and a modern Jeep will not stay running when the battery is dead or too low. Before buying anything use a bench charger to charge the battery overnight. The days of an engine being able to run with a dead or nearly dead battery are long gone. That's because modern alternators like our TJs have require 12v from the battery for the alternator's exciter circuit. And no, the alternator is not capable of recharging its battery when the battery is too low or dead.
 
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Jerry Bransford said:
A hour or so is not long enough to charge the battery, and a modern Jeep will not stay running when the battery is dead or too low. Before buying anything use a bench charger to charge the battery overnight. The days of an engine being able to run with a dead or nearly dead battery are long gone. That's because modern alternators like our TJs have require 12v from the battery for the alternator's exciter circuit. And no, the alternator is not capable of recharging its battery when the battery is too low or dead.
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I had to jump start my 2001 4.0 the other morning. The battery wasn’t completely dead but it didn’t have enough juice to turn it over to start. Got it running but it wouldn’t hold an idle. I fully charged the battery over night and it started right up the next morning. It idled fine for about 2 miles then died. I tested the battery and my tester read 12.4V.

I thought 12v was enough to hold an idle. What could be causing my Jeep to stall? It ran fine before the battery issue.
 
Using a common volt meter won't properly test a battery. Even a bad/nearly dead battery can measure 12 volts. It needs to be "load tested" with a special volt meter that places a heavy electrical load (half the battery's CCA rating) on the battery and measures the voltage after no less than 15 seconds with the heavy load on it. Most auto parts stores can load test it but done improperly it can indicate the battery is good when in fact it's bad. If that's where you take make sure they hold the load on for at least 15 seconds before making the voltage measurement. Better, go to a battery specialty store for the load test, its employees are far more likely to know how to properly conduct a load test.

And to sure, no TJ will idle or run for long when the battery is too low/dead. The alternator requires 12 volts from the battery to be able to generate power, like for the ignition system.
 
Jerry Bransford said:
Using a common volt meter won't properly test a battery. Even a bad/nearly dead battery can measure 12 volts. It needs to be "load tested" with a special volt meter that places a heavy electrical load on the battery and measures the voltage after no less than ten seconds with the heavy load on it. Most auto parts stores can load test it but done improperly it can indicate the battery is good when in fact it's bad. If that's where you take make sure they hold the load on for at least ten seconds before making the voltage measurement. Better, go to a battery specialty store for the load test, its employees are far more likely to know how to properly conduct a load test.
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Thank you, Jerry.

The battery is less than a year old. It’s a Duralast Gold. Not the greatest but it certainly seems like it should’ve lasted longer. I installed a winch and had an ARB compressor installed after I got the battery. Could just having those connected to the battery contributed to premature draining?
 
One more thing to try... physically remove both battery connections and wire brush them and the battery posts. Then securely reinstall them tightly. A loose/dirty/corroded/weak battery connection can cause problems like this.
 
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Took my battery back to Autozone and then BatteriesPlus. Both informed me the battery is fine.

Just to recap, my Jeep needed a jump start last week. Charged it overnight and now it starts right up, idles and drives fine for about 10-15 minutes. After 10-15 minutes it won’t hold an idle and dies.

Connections are clean and tight. Any thoughts and what is causing this?
 
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