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Old 10-08-2015, 09:21 AM
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98 ZJ Stalling at stop lights.

Hello, I am Jesse!
I am new to the forum. I found what seems to be an amazing deal on a 1998 jeep grand cherokee Laredo 4.0l. I found this really clean rust free ZJ up for sale for $600 it needed door pins and the engine was randomly stalling at stop lights. I bought it to repair hoping that it will be an easy fix and if not I can still get most of my money back so it is worth the gamble. So I bought it and drove it home on a 45 minute drive and it ran and drove perfectly, actually it was one of the smoothest vehicles I have ever driven. the next time I drove it about 5 hours later It started doing the stalling at stop sign thing. At stop signs it will shutter at low RPMs and then stall at really low RPMS. If you keep your foot on the gas and keep the RPMs above 1000 it runs fine. I have done some research and people that have had similar problems say it could be any of the following:

IAC
TPS
Crank Position Sensor
fuel pump/filters
vacuum leaks
distributor cap,rotor and wires
PCM
PCM bolts
Torque converter/torque converter clutch
Transmission solenoids/ Speed Sensor

So far I have replaced the Idle Air Control valve and the Throttle Position Sensor. I have checked some lines and fixed some possible vacuum leaks. I want to know if anyone has had a similar issue and knows what could be the most likely solution. Before this zj I had a v8 and it had the same issue with a different engine and I changed multiple sensors and never got rid of the issue before I got rid of it. The odd thing is that in park the jeep will run well. Sometimes in park the rpms will increase and sometimes it sounds like it will miss but it will never stall. Sometimes (rarely) the jeep just runs great, no stalling or anything. I have to think the engine isnt crap because it runs well over 1000 rpms and whenever it doesnt feel like stalling. Please someone help me before I spend too much money fixing this issue which will ultimately make this a bad deal.

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  #2  
Old 10-08-2015, 04:38 PM
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Re: 98 ZJ Stalling at stop lights.

Welcome to the garage.
You did change the IAC stepper motor, but did you also clean the air canal. Over time dirt will settle on the walls of the canal, restricting the airflow, even if the stepper motor pintle opens ompletely. It can still have enough air to idle when in Park, but the higher power needed when in D can be too much.
It can also be that the torque converter clutch doesnt release completely, causing a drag on the engine and making it to stall
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Old 10-08-2015, 04:44 PM
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Re: 98 ZJ Stalling at stop lights.

Quote:
Originally Posted by JESSE98ZJ View Post
Hello, I am Jesse!
I am new to the forum. I found what seems to be an amazing deal on a 1998 jeep grand cherokee Laredo 4.0l. I found this really clean rust free ZJ up for sale for $600 it needed door pins and the engine was randomly stalling at stop lights. I bought it to repair hoping that it will be an easy fix and if not I can still get most of my money back so it is worth the gamble. So I bought it and drove it home on a 45 minute drive and it ran and drove perfectly, actually it was one of the smoothest vehicles I have ever driven. the next time I drove it about 5 hours later It started doing the stalling at stop sign thing. At stop signs it will shutter at low RPMs and then stall at really low RPMS. If you keep your foot on the gas and keep the RPMs above 1000 it runs fine. I have done some research and people that have had similar problems say it could be any of the following:

IAC
TPS
Crank Position Sensor
fuel pump/filters
vacuum leaks
distributor cap,rotor and wires
PCM
PCM bolts
Torque converter/torque converter clutch
Transmission solenoids/ Speed Sensor

So far I have replaced the Idle Air Control valve and the Throttle Position Sensor. I have checked some lines and fixed some possible vacuum leaks. I want to know if anyone has had a similar issue and knows what could be the most likely solution. Before this zj I had a v8 and it had the same issue with a different engine and I changed multiple sensors and never got rid of the issue before I got rid of it. The odd thing is that in park the jeep will run well. Sometimes in park the rpms will increase and sometimes it sounds like it will miss but it will never stall. Sometimes (rarely) the jeep just runs great, no stalling or anything. I have to think the engine isnt crap because it runs well over 1000 rpms and whenever it doesnt feel like stalling. Please someone help me before I spend too much money fixing this issue which will ultimately make this a bad deal.
I'd check the CPS. You should be able to get a Factory Service Manual from TechAuthority or eBay for how to do so, or watch for Frango answers.

You left off fuel pressure regulator and O2 Sensors and Catalysts.
There is probably a reason for the $600 price--they usually go for at least $1500 or more.

If you were in Los Angeles, I'd suspect crappy gas, or that stuff they sell as gas.

Pick up a scan tool and see if it would be kind enough to leave any fault codes that could narrow it down a bit.

I'd also run a can or so of Seafoam thru it in case the valves are all crudded up. That engine needs to be run to roughly 3500 every now and then to have the valve rotation work.
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Old 11-17-2015, 09:19 AM
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Re: 98 ZJ Stalling at stop lights.

I ended up cleaning the throttle body and eliminating any possible vacuum leaks and changed the throttle position sensor, crank position sensor, and Idle air control valve and the Jeep has been running great for a month in all conditions so I feel comfortable saying that this issue is now fixed. Thanks for the input everyone. I apologize for not being able to pinpoint exactly which item fixed the issue but I only put about $170 into fixing it and about half an hour of work changing the parts. I just felt I needed to tell everyone what I did to fix the problem because I hate reading forums that have the exact issue I am having and no one ever tells us what worked to fix their issue. Hope this helps someone.
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Old 08-28-2016, 12:42 AM
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Re: 98 ZJ Stalling at stop lights.

Quote:
Originally Posted by JESSE98ZJ View Post
I ended up cleaning the throttle body and eliminating any possible vacuum leaks and changed the throttle position sensor, crank position sensor, and Idle air control valve and the Jeep has been running great for a month in all conditions so I feel comfortable saying that this issue is now fixed. Thanks for the input everyone. I apologize for not being able to pinpoint exactly which item fixed the issue but I only put about $170 into fixing it and about half an hour of work changing the parts. I just felt I needed to tell everyone what I did to fix the problem because I hate reading forums that have the exact issue I am having and no one ever tells us what worked to fix their issue. Hope this helps someone.


I appreciate the update. I've been having some stalling issues with my 97 4.0L ZJ. I get a misfire in cylinder 2 error code but my me again couldn't get it to stall once I drove the 20 miles to his shop. At least I can suggest the fix you identified. Thanks again.
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