Rough Cold Idle - JeepForum.com
 2Likes
  • 1 Post By Timo_90xj
  • 1 Post By jtec
 
LinkBack Thread Tools
post #1 of 7 Old 02-21-2020, 07:13 AM Thread Starter
paulvon
Registered User
 
Join Date: Jun 2018
Posts: 221
Rough Cold Idle

On my 97 ZJ 4.0 the idle is rough and it is temperature dependent.

50 deg F starts without issue
40 deg F starts but seems like it wants to stall
30 deg F have to give it gas to prevent stalling

Jeep runs fine after it has fully warmed up.

Currently there are no codes or pending codes.

A few months ago replaced the idle air controlled and cleaned the throttle body.

This is a new behavior. Worked fine earlier in the winter.

Could it be the IAC again just without a code or something else?

Sent from my SM-G920V using Tapatalk


1997 ZJ 4.0 L - Upgraded to heavy 93 sway bar
2004 WJ 4.7 L - 2 1/2" lift
2011 KK 3.7 L
paulvon is offline  
Sponsored Links
Advertisement
 
post #2 of 7 Old 02-21-2020, 09:34 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: 10,303
I'd suspect coolant temp sensor and/ or intake air temp sensor.

On a 1997 you can easily check those with a code reader that supports live mode; when the engine hasn't been started -> plug in the reader -> turn ignition key to run (key on, engine off) -> check in the live mode what the intake air temp and coolant temps show.
jtec likes this.

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 #3 of 7 Old 02-27-2020, 06:18 AM Thread Starter
paulvon
Registered User
 
Join Date: Jun 2018
Posts: 221
Have been checking the temps for the past few days and everything looks fine.

Still having the idle issue.

Sent from my SM-G920V using Tapatalk

1997 ZJ 4.0 L - Upgraded to heavy 93 sway bar
2004 WJ 4.7 L - 2 1/2" lift
2011 KK 3.7 L
paulvon is offline  
 
post #4 of 7 Old 02-29-2020, 10:05 AM
8v-of-fury
Registered User
1998 ZJ 
 
Join Date: Nov 2015
Location: Orillia
Posts: 499
30f isnt even cold, and no (gasoline) EFI should have a problem starting at that temp.

The fact that it starts better warmer gives us an idea that it is not over fueling.. as that would help when colder.

When you pedal in some throttle (air) does it run proper?

Basically it takes a real world temp from the CTS or IAT to give itself a base fuel map to start with. That's an odd one.

Both those sensors show cold what the actual outside temps are?

'98 ZJ 4.0/242, Locked d30/d35, 31x10.5x15, 2" BB w/ Bilstein 5100's
8v-of-fury is offline  
post #5 of 7 Old 02-29-2020, 10:20 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: 10,303
Quote:
Originally Posted by paulvon View Post
Have been checking the temps for the past few days and everything looks fine.

Still having the idle issue.
Did you check the live data from the OBD2 port with a code reader? How did the temperature sensor temps - we need to know BOTH the coolant and intake air temps - look like in relation to outside air temp and engine running a while?
We also need to know what the coolant and intake air temps are BEFORE you fire up the Jeep and what the outside air temperature is at the same time.

These things fire up and idle like nothing at -25F and way colder than that, I know from personal experience. Since your issue is outside temperature- related, it must have something to do with how the PCM tries - or in this case does not - adjust to different temps.

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 #6 of 7 Old 02-29-2020, 12:32 PM
jtec
Web Wheeler
 
jtec's Avatar
2014 JK Wrangler 
 
Join Date: Oct 2017
Posts: 7,595
A scanner makes quick work of diagnosing I would also look at fuel trims and o2 readings.

No scanner- try looking at
spark plugs, wet, BLACK, dry, tan?
What is fuel pressure PSI?
engine vacuum?
Timo_90xj likes this.

When I see the price of OEM I think aftermarket.
When I see the quality of aftermarket I think OEM.
jtec is online now  
post #7 of 7 Old 03-01-2020, 10:57 AM
terpsmandan
Registered User
1998 ZJ 
 
Join Date: Sep 2009
Location: Penn Yan, NY
Posts: 1,385
I was having an issue with the 98 4.0. When cold it would start fine but if you had to shift from reverse to drive it would stall and be very difficult to get restarted. Replaced the cap, rotor and plugs and the issue is gone. How long has it been since you replaced the cap and rotor?
terpsmandan 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