ZJ Dies When Idle - JeepForum.com
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post #1 of 16 Old 06-29-2019, 05:08 PM Thread Starter
RepBolt
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1997 ZJ 
 
Join Date: Jun 2017
Location: Bay Area
Posts: 94
ZJ Dies When Idle

I just got my 97 ZJ 5.2L with 166k miles back from the auto shop after doing a full tune up and replaced a bunch of parts. My mechanic told me I have bad shocks and a bad transfer case. I knew about both and already had plans to do a 4.5" lift and get a new VC for my 249 (don't want to swap TC). I drove my ZJ for about 15 miles after I picked it up, and it would die on me when I was idle either at a stop sign or stop light. It died about 7x throughout my drive, and I'd say about 75% of the time I came to a stop it died on me. I went back to my mechanic and told him about the issue, and he said it was due to the bad transfer case. However, prior to me bringing my ZJ to the shop to get repaired, I didn't experience my ZJ dying on me when I came to a stop at all. I hardly drove it, but even then it never died on me and I certainly drove it more than 15 miles before I dropped it off to my mechanic. It only died when I got it back from the shop.

Here is a list of parts I got installed:
  • Oil Pan
  • Water Pump Stud Kit
  • Oil Pan Gasket
  • Valve Cover Gasket
  • Water Pump Gasket
  • Water Pump
  • Belt
  • Idler Pulley
  • Belt Tensioner
  • Radiator Fan Clutch
  • Oil Pump
  • Oil Filter
  • Crankshaft Seal (Rear)
  • Crankshaft Seal (Front)
  • Transmission Mount
  • Motor Mount
  • Plenum Kit
  • Timing Chain Kit
  • Heater Hose
  • Thermostat
  • Water Flange Gasket
  • Timing Cover Gasket

That said, can a bad TC cause your ZJ to die when idle or is this an issue that was caused by one of the parts being installed? I also noticed a hose hanging down underneath my engine and my mechanic said that was for the shocks to let air in. I'm not at all a mechanic so I went with whatever my mechanic told me because I've been going to him for quite some time now and I trust him. I just want another opinion from actual people who know the ZJ.

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post #2 of 16 Old 06-29-2019, 07:04 PM
FlamingRain
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1998 ZJ 
 
Join Date: Jun 2011
Location: Ellensburg
Posts: 210
Check battery terminals and especially grounds. Any vehicle, if the grounds are even a little dirty can cause some random BS to start happening, including stalling when idle.

2wd can really get you places you can't get out of without 4lo. - Ratmonkey
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post #3 of 16 Old 06-30-2019, 09:18 AM
riverzj
Registered User
 
Join Date: May 2018
Posts: 93
Does it studder and die or just die like you shut if off. If it studders itís something like IAC or FPR or fuel pump/filter. Otherwise probably electrical and wouldnít be suprised if it was the crankpositionsensor thatís what was bad on mine and I had that happen where it would just shut off.


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post #4 of 16 Old 06-30-2019, 09:32 AM
firebane
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1998 ZJ 
 
Join Date: Sep 2018
Location: Calgary
Posts: 317
Quote:
Originally Posted by RepBolt View Post
I just got my 97 ZJ 5.2L with 166k miles back from the auto shop after doing a full tune up and replaced a bunch of parts. My mechanic told me I have bad shocks and a bad transfer case. I knew about both and already had plans to do a 4.5" lift and get a new VC for my 249 (don't want to swap TC). I drove my ZJ for about 15 miles after I picked it up, and it would die on me when I was idle either at a stop sign or stop light. It died about 7x throughout my drive, and I'd say about 75% of the time I came to a stop it died on me. I went back to my mechanic and told him about the issue, and he said it was due to the bad transfer case. However, prior to me bringing my ZJ to the shop to get repaired, I didn't experience my ZJ dying on me when I came to a stop at all. I hardly drove it, but even then it never died on me and I certainly drove it more than 15 miles before I dropped it off to my mechanic. It only died when I got it back from the shop.

Here is a list of parts I got installed:
  • Oil Pan
  • Water Pump Stud Kit
  • Oil Pan Gasket
  • Valve Cover Gasket
  • Water Pump Gasket
  • Water Pump
  • Belt
  • Idler Pulley
  • Belt Tensioner
  • Radiator Fan Clutch
  • Oil Pump
  • Oil Filter
  • Crankshaft Seal (Rear)
  • Crankshaft Seal (Front)
  • Transmission Mount
  • Motor Mount
  • Plenum Kit
  • Timing Chain Kit
  • Heater Hose
  • Thermostat
  • Water Flange Gasket
  • Timing Cover Gasket

That said, can a bad TC cause your ZJ to die when idle or is this an issue that was caused by one of the parts being installed? I also noticed a hose hanging down underneath my engine and my mechanic said that was for the shocks to let air in. I'm not at all a mechanic so I went with whatever my mechanic told me because I've been going to him for quite some time now and I trust him. I just want another opinion from actual people who know the ZJ.

When I have was having idle issues and idle issues to the point it would stall.. I replaced the map sensor and all issues went away.
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post #5 of 16 Old 06-30-2019, 10:13 AM
Roadtripguy
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1996 ZJ 
 
Join Date: Aug 2014
Location: Fairfield County
Posts: 180
If I had an issue like this, ESPECIALLY right after having a bunch of stuff replaced at the shop, the very first thing I would check would be the vacuum lines, and I'd go over all of them with a fine tooth comb.
Benthal8 likes this.
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post #6 of 16 Old 06-30-2019, 10:30 AM
V8GCZJ
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Join Date: Sep 2018
Posts: 329
The mechanic probably disconnected the battery cable. When doing so it clears the memory in the pcm. After reconnection the pcm needs to relearn the sensors(and the IAC/idle). Does it stall when in park after you start it/rev it? Wouldn't hurt to clean the throttle body and IAC port. Carbon builds up in there and can cause idle issues.
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post #7 of 16 Old 07-01-2019, 12:59 AM
BRBauer2
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1997 ZJ 
 
Join Date: Mar 2019
Location: Chicago
Posts: 103
My random stalling issues were solved by replacing the ignition coil.

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post #8 of 16 Old 07-02-2019, 11:00 PM Thread Starter
RepBolt
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1997 ZJ 
 
Join Date: Jun 2017
Location: Bay Area
Posts: 94
This is all wonderful feedback that I'll need to look into once I have some time with my ZJ.
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post #9 of 16 Old 07-03-2019, 11:52 AM
HighLonesome
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1995 ZJ 
 
Join Date: Feb 2005
Location: New Mexico
Posts: 8,056
I did this on all my ZJs when I bought them..
disconnect the battery.
remove the TB, remove all sensors (anything non-metal) from TB

get a gallon of carb cleaner and soak the TB overnight
scrub the entire TB clean, make sure you get all the tiny passages, use a single strand of copper wire for the smallest ones
clean the IAC plunger, do not disturb it's position

inspect/replace the small hose for the MAP
reinstall everything and inspect all the hoses/fittings/tees/unions that connect to the TB
start up, let her idle to operating temp
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post #10 of 16 Old 07-05-2019, 11:05 AM Thread Starter
RepBolt
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1997 ZJ 
 
Join Date: Jun 2017
Location: Bay Area
Posts: 94
Quote:
Originally Posted by BRBauer2 View Post
My random stalling issues were solved by replacing the ignition coil.

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What ignition coil do you recommend? I'm thinking the NGK 48812 {#U1086} NGK HEI, but I plan to run CHAMPION 9203 Iridium spark plugs, and wondering if they'll work well together.
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post #11 of 16 Old 07-05-2019, 02:02 PM
HighLonesome
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1995 ZJ 
 
Join Date: Feb 2005
Location: New Mexico
Posts: 8,056
I bet they run great together. I'm running iridium plugs in my 5.2 and 5.9, both running great. Not sure why the coil says HEI, I think it's just a standard replacement.
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post #12 of 16 Old 07-05-2019, 02:57 PM
paulsheer2
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1993 ZJ 
 
Join Date: Apr 2016
Posts: 1,213
Garage
1. idle air control servo
2. clean out IAC hole with carb cleaner and toothbrush until there is no black in there at all
3. install extra ground from engine to battery and body
4. engine temp sensor wires (rewire from ecu)
5. switch to MSD ignition and MSD coil
6. install extra bung for aftermarket AFR test dial

93 ZJ 5.2, 3.58 stroked. 242 swap. 2.5" lift. dozens of mods.
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post #13 of 16 Old 07-05-2019, 08:10 PM Thread Starter
RepBolt
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1997 ZJ 
 
Join Date: Jun 2017
Location: Bay Area
Posts: 94
Quote:
Originally Posted by HighLonesome View Post
I bet they run great together. I'm running iridium plugs in my 5.2 and 5.9, both running great. Not sure why the coil says HEI, I think it's just a standard replacement.
This is the ignition coil I was referring to. The description says "HEI", but it's under "Standard Replacement" in RockAuto.
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post #14 of 16 Old 07-05-2019, 09:06 PM
BRBauer2
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1997 ZJ 
 
Join Date: Mar 2019
Location: Chicago
Posts: 103
Quote:
Originally Posted by RepBolt View Post
What ignition coil do you recommend? I'm thinking the NGK 48812 {#U1086} NGK HEI, but I plan to run CHAMPION 9203 Iridium spark plugs, and wondering if they'll work well together.
Standard Motor Products UF97T Ignition Coil https://smile.amazon.com/dp/B004BTQ7..._sabiDbHE62ZKX

I went with that one. Installed almost 2 months ago and no issues yet.

4.0 engine

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post #15 of 16 Old 07-07-2019, 11:10 PM Thread Starter
RepBolt
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1997 ZJ 
 
Join Date: Jun 2017
Location: Bay Area
Posts: 94
Does anyone know if the Champion Iridium 9203 {#RC12WLPB4} Spark Plugs from RockAuto come pre-gapped to .040?
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