Old problem returning (stalling when hot restart) - JeepForum.com
 
LinkBack Thread Tools
post #1 of 14 Old 05-19-2020, 09:32 PM Thread Starter
Maverickxeo
Registered User
 
Maverickxeo's Avatar
2002 TJ Wrangler 
 
Join Date: Jan 2010
Location: Wetaskiwin
Posts: 2,631
Garage
Old problem returning (stalling when hot restart)

Today, my 94 5.2L ZJ stalled after a long drive (I travelled about 40km or so at highway speeds, and then did a lot of 'crawling' speeds - 20km/hour or so for a good while). The ambient temperature here was about 16C - so not very warm.

Basically, it drove fine, idled fine, etc., until I stopped the vehicle. Gauges were all looking good - no issues presented themselves. After about 10 minutes of the vehicle being parked, I started it - it started normally (very well), except the RPMs slowly dropped and it stalled out. The 'stall' was very smooth - there was no missing or shaking (I actually didn't notice it stalled for a few seconds until I tried to move it!). I started it again - and it did it again. It did this a few times, until I gave it a little gas (VERY little - RPMs were less than 1000) and it ran smooth. Took my foot off the gas and it slowly dropped and stalled again.

At that point, I put the vehicle in neutral, left foot on brake and right lightly on gas again. I put the transmission into gear (probably not good, I know, haha!) and then it was fine driving. I drove about 50 feet and had to stop and let it idle in gear. It ran fine.

I got on the highway and stopped for gas after about 15 minutes - no problems until I tried to start it - it did the same thing. This time, while driving slowly, it would stall out on me when RPMs were low (for a short while - it gradually got better the longer I drove it). After a few minutes, I got back on the highway and headed home.

I got home, and shut off the engine to get mail (community box). Got back in after a few seconds, and it stalled again. Got it back home (less than a block), and I tried to let it 'stall' but it continued to idle fine. I checked codes, and just got 55 (all clear?).

My first thought is fuel vapour lock - is that possible? If not, where should I look next? Fuel pressure is good, air filter is newish - engine compression is within spec.

Maverickxeo is offline  
Sponsored Links
Advertisement
 
post #2 of 14 Old 05-19-2020, 11:57 PM
Zilliver
Registered User
1998 ZJ 
 
Join Date: Sep 2015
Location: Vantaa <-> Tallinn
Posts: 584
There is no fuel vapour lock problem on the V8.

But its seems to be your IAC - have you cleaned it or changed it? Is it aftermarket crap or Mopar?

How clean is the throttle valve?

98 Grand Cherokee 5.9 - daily
95 Grand Cherokee 5.2 - offroad
Zilliver is offline  
post #3 of 14 Old 05-20-2020, 01:23 AM
Timo_90xj
Web Wheeler
 
Timo_90xj's Avatar
1998 ZJ 
 
Join Date: Mar 2006
Location: Helsinki, Finland - on the European side of the Atlantic
Posts: 10,385
IAC controls idle between certain range, but if engine is at runnung temp, unplugging IAC connector and then firing up the engine it should run. If not, there is something else wrong than your IAC. In other words, V8 throttle body is factory- adjusted in a way that the IAC is not setting the base RPMs for idle.

If you're using a DRB3, Snap-on MT2500 or equivalent, if I remember correctly IAC count should show something like 40-60 at idle - this with the TB fuel vapor purge vacuum port and IAC air channel plugged with your thumb.
There is the FSM method using the fixed orifice tube and the DRB3 (MT2500 IIRC can also perform idle test), which is the best way to diagnose.

Checking the base idle manually "DIY- style":
* Bring the engine to running temp.
* Shut off engine, unplug IAC connector, then fire up the engine.
* Plug the IAC channel and fuel tank vapor purge vacuum line nipple on the throttle body - you should be sitting at around 800rpms +/-50rpms.
* Base idle can be adjusted with removing the adjuster screw plug on the TB, but there should be no need to do this with a stock engine.

Do note that using the DIY method on checking/ adjusting the base idle isn't 100% accurate, and if you adjust base idle screw on the TB based on the DIY manual test you can mess things up regarding idle control and how the engine behaves under certain conditions.

1998 Grand Cherokee 5.9 LX daily driver, 1.75" BB, 32" KM2s, HPD30 Eaton e-locker/D44a stock LSD, 4.56 gears, custom- fabbed tube bumpers and tube fenders,...


To view links or images in signatures your post count must be 10 or greater. You currently have 0 posts.



1990 XJ Limited (4-door), 4.0 I6, AW4, NP242, ***rolled and totalled @ 165k miles***

***Under construction***
1990 XJ (4-door), 4.0 I6, AW4, NP242, PBR 42" tires, Unimog 404 portal axles, 110" WB, full cage + uniframe completely rebuilt, front 3-link + panhard / double triangulated 4-link rear,... ***SOLD***
Timo_90xj is offline  
 
post #4 of 14 Old 05-20-2020, 11:00 AM Thread Starter
Maverickxeo
Registered User
 
Maverickxeo's Avatar
2002 TJ Wrangler 
 
Join Date: Jan 2010
Location: Wetaskiwin
Posts: 2,631
Garage
Quote:
Originally Posted by Timo_90xj View Post
IAC controls idle between certain range, but if engine is at runnung temp, unplugging IAC connector and then firing up the engine it should run. If not, there is something else wrong than your IAC. In other words, V8 throttle body is factory- adjusted in a way that the IAC is not setting the base RPMs for idle.
I will have to try that next time.

Quote:
Originally Posted by Zilliver View Post
There is no fuel vapour lock problem on the V8.

But its seems to be your IAC - have you cleaned it or changed it? Is it aftermarket crap or Mopar?

How clean is the throttle valve?
IAC is Mopar as far as I know - throttle body and IAC SHOULD BE clean - I cleaned them last year.
Maverickxeo is offline  
post #5 of 14 Old 05-20-2020, 07:01 PM
PolkaPower
Registered User
 
PolkaPower's Avatar
1998 ZJ 
 
Join Date: Aug 2011
Location: The Abyss
Posts: 22,807
If it only does it when at operating temp it might be a failing 02 sensor.

Sent from my BND-L24 using Tapatalk
PolkaPower is online now  
post #6 of 14 Old 05-20-2020, 07:05 PM Thread Starter
Maverickxeo
Registered User
 
Maverickxeo's Avatar
2002 TJ Wrangler 
 
Join Date: Jan 2010
Location: Wetaskiwin
Posts: 2,631
Garage
Quote:
Originally Posted by PolkaPower View Post
If it only does it when at operating temp it might be a failing 02 sensor.

Sent from my BND-L24 using Tapatalk
O2 Sensor is a newish NTK brand.

I checked the IAC while getting hot - I left it idle for quite some time to get hot, and shut it off. First attempt at restarting (with IAC connected), it stalled. I tried it a second time, and it didn't stall. Tried it several times with the IAC disconnected and it ran fine without it. Throttle plates are also spotless so I am assuming IAC is as well (cleaned them both at the same time).

I did test to see if the IAC actually adjusted RPM - based on the tachometer, I did NOT see any increase in RPM with it connected when running AC (clutch running) and/or headlights on. With the IAC disconnected, it doesnt change either (as expected). Putting the vehicle in gear (reverse or drive), the RPM drops from idle (500ish RPM) to about 250ish RPM with or without IAC connected.
Maverickxeo is offline  
post #7 of 14 Old 05-20-2020, 10:26 PM
Timo_90xj
Web Wheeler
 
Timo_90xj's Avatar
1998 ZJ 
 
Join Date: Mar 2006
Location: Helsinki, Finland - on the European side of the Atlantic
Posts: 10,385
500rpms with the IAC disconnected, engine at running temp, A/C on and transmission in park/ neutral is way too low. It should be at around 800rpms +/-50.

Normal idle with IAC connected is around 850-900.

1998 Grand Cherokee 5.9 LX daily driver, 1.75" BB, 32" KM2s, HPD30 Eaton e-locker/D44a stock LSD, 4.56 gears, custom- fabbed tube bumpers and tube fenders,...


To view links or images in signatures your post count must be 10 or greater. You currently have 0 posts.



1990 XJ Limited (4-door), 4.0 I6, AW4, NP242, ***rolled and totalled @ 165k miles***

***Under construction***
1990 XJ (4-door), 4.0 I6, AW4, NP242, PBR 42" tires, Unimog 404 portal axles, 110" WB, full cage + uniframe completely rebuilt, front 3-link + panhard / double triangulated 4-link rear,... ***SOLD***
Timo_90xj is offline  
post #8 of 14 Old 05-20-2020, 10:40 PM Thread Starter
Maverickxeo
Registered User
 
Maverickxeo's Avatar
2002 TJ Wrangler 
 
Join Date: Jan 2010
Location: Wetaskiwin
Posts: 2,631
Garage
Quote:
Originally Posted by Timo_90xj View Post
500rpms with the IAC disconnected, engine at running temp, A/C on and transmission in park/ neutral is way too low. It should be at around 800rpms +/-50.

Normal idle with IAC connected is around 850-900.
So what would you suspect I look into? Could it be MAP or TPS?

EDIT: Or should I do the 'manual' idle setting? I don't want to, but if I need to I can do it.
Maverickxeo is offline  
post #9 of 14 Old Yesterday, 11:07 AM Thread Starter
Maverickxeo
Registered User
 
Maverickxeo's Avatar
2002 TJ Wrangler 
 
Join Date: Jan 2010
Location: Wetaskiwin
Posts: 2,631
Garage
So in the middle of the night, I remembered I forgot something, haha!

Sometimes when the engine is cold (hasn't ran for a while), the engine will crank without starting. It will do this with or without leaving the key in the on position for 20 seconds. The only 'cure' is to hold the throttle a bit (maybe mid throttle at most?). After it starts, as soon as I let off the throttle, it idles and runs fine. It does NOT do this every cold start either - it's very random. Is this possibly related?
Maverickxeo is offline  
post #10 of 14 Old Yesterday, 01:14 PM
jeepjeepster
Registered User
 
Join Date: Dec 2004
Posts: 3,564
I'm curious, you say the engine rpms do not change with or without the IAC connected, do you not think the IAC is bad?

1994 ZJ-I6 w/216,000 mi
1998 ZJ 5.9 w/65,155 mi Slate Black
2004 KJ w/90,300 mi
jeepjeepster is offline  
post #11 of 14 Old Yesterday, 01:54 PM
Timo_90xj
Web Wheeler
 
Timo_90xj's Avatar
1998 ZJ 
 
Join Date: Mar 2006
Location: Helsinki, Finland - on the European side of the Atlantic
Posts: 10,385
Quote:
Originally Posted by jeepjeepster View Post
I'm curious, you say the engine rpms do not change with or without the IAC connected, do you not think the IAC is bad?
Read above what I wrote regarding V8 IAC and idle base adjustment. IAC of course should adjust if RPMs are too low, but its function is not to compensate for way too low base idle.
IAC should adjust for a number of things when RPMs drop low (cold starts, A/C compressor on/off, decelaration, etc.).
If idle base adjustment is incorrect, you get "throttle hover" and other somewhat weird issues.

It helps a lot in diagnosing idle issues if you have a scanner that is able to show IAC operation.

1998 Grand Cherokee 5.9 LX daily driver, 1.75" BB, 32" KM2s, HPD30 Eaton e-locker/D44a stock LSD, 4.56 gears, custom- fabbed tube bumpers and tube fenders,...


To view links or images in signatures your post count must be 10 or greater. You currently have 0 posts.



1990 XJ Limited (4-door), 4.0 I6, AW4, NP242, ***rolled and totalled @ 165k miles***

***Under construction***
1990 XJ (4-door), 4.0 I6, AW4, NP242, PBR 42" tires, Unimog 404 portal axles, 110" WB, full cage + uniframe completely rebuilt, front 3-link + panhard / double triangulated 4-link rear,... ***SOLD***
Timo_90xj is offline  
post #12 of 14 Old Yesterday, 03:55 PM Thread Starter
Maverickxeo
Registered User
 
Maverickxeo's Avatar
2002 TJ Wrangler 
 
Join Date: Jan 2010
Location: Wetaskiwin
Posts: 2,631
Garage
So a little update. Went for a drive and it did the same thing. I did disconnect the IAC and it ran (low RPM - but it ran). Plugged it back in, and started it with the same stalling happening. I repeated this a few times back and forth and it was very consistently showing that with it connected it would stall; disconnected it would run.

Thanks for the advice!
Maverickxeo is offline  
post #13 of 14 Old Yesterday, 06:06 PM
jeepjeepster
Registered User
 
Join Date: Dec 2004
Posts: 3,564
Quote:
Originally Posted by Timo_90xj View Post
Read above what I wrote regarding V8 IAC and idle base adjustment. IAC of course should adjust if RPMs are too low, but its function is not to compensate for way too low base idle.
IAC should adjust for a number of things when RPMs drop low (cold starts, A/C compressor on/off, decelaration, etc.).
If idle base adjustment is incorrect, you get "throttle hover" and other somewhat weird issues.

It helps a lot in diagnosing idle issues if you have a scanner that is able to show IAC operation.
But if its not changing the rpms at all, then I would believe something is wrong with it. Even if the base rpms should be higher, do you not believe it should try to bring the rpms up when plugged in?

1994 ZJ-I6 w/216,000 mi
1998 ZJ 5.9 w/65,155 mi Slate Black
2004 KJ w/90,300 mi
jeepjeepster is offline  
post #14 of 14 Old Today, 04:22 AM
Timo_90xj
Web Wheeler
 
Timo_90xj's Avatar
1998 ZJ 
 
Join Date: Mar 2006
Location: Helsinki, Finland - on the European side of the Atlantic
Posts: 10,385
Of course IAC should try to adjust. I'm sure there isn't just a single issue here, being that idle rpms are too low with IAC disconnected, and IAC plugged in rpms don't change and the engine dies.

Live data would help a ton, but this being an OBD1 a normal scanner won't work

1998 Grand Cherokee 5.9 LX daily driver, 1.75" BB, 32" KM2s, HPD30 Eaton e-locker/D44a stock LSD, 4.56 gears, custom- fabbed tube bumpers and tube fenders,...


To view links or images in signatures your post count must be 10 or greater. You currently have 0 posts.



1990 XJ Limited (4-door), 4.0 I6, AW4, NP242, ***rolled and totalled @ 165k miles***

***Under construction***
1990 XJ (4-door), 4.0 I6, AW4, NP242, PBR 42" tires, Unimog 404 portal axles, 110" WB, full cage + uniframe completely rebuilt, front 3-link + panhard / double triangulated 4-link rear,... ***SOLD***
Timo_90xj is offline  
Reply

Quick Reply
Message:
Options

Register Now



In order to be able to post messages on the JeepForum.com forums, you must first register.
Please enter your desired user name, your email address and other required details in the form below.

User Name:
Password
Please enter a password for your user account. Note that passwords are case-sensitive.

Password:


Confirm Password:
Email Address
Please enter a valid e-mail address for yourself.



Email Address:
OR

Log-in











Currently Active Users Viewing This Thread: 1 (0 members and 1 guests)
 
Thread Tools
Show Printable Version Show Printable Version
Email this Page Email this Page



Posting Rules  
You may post new threads
You may post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are On
Refbacks are On

 
For the best viewing experience please update your browser to Google Chrome