2001 XJ, VERY LOW or won't idle after warm
#1
Junior Member
Thread Starter
Join Date: Sep 2012
Location: Brevard, NC
Posts: 49
Likes: 0
Received 0 Likes
on
0 Posts
Year: 2001
Model: Cherokee
Engine: 4.0
![Default](https://www.cherokeeforum.com/images/icons/icon1.gif)
Last week my 2001 XJ with 190,000 miles just started idling very low or stalling out after it gets warm. Pulling up to a redlight, it will idle down to 200-250 rpms and/or stall out. It idles fine when first cranked cold, even if I have it warming up for 5 minutes or so in the mornings. I'm getting by currently by just giving it enough gas when stopped to hold the rpms around 1000. Otherwise it drives pretty normal and I don't notice any other issues. Tail pipe shows signs that it might be running a tad rich.
Check engine light hasn't come on yet. I have replaced the crank position sensor a couple times in the last year-year and half. Could it be that going out again or anyone have an idea if it could be another sensor? I don't currently own an OBD scan tool, probably should though. Have been borrowing one from a friend when needed. Did also replace the IAC valve about a year ago too.
I haven't pulled plugs to check them yet either, but I did replace coils, wires, and plugs about 15,000-20,000 miles ago.
Any ideas before I start blindly replacing sensors or just take it to my trusted mechanic (who is always swamped with work)? Or recommendations on which sensors you would start with?
Check engine light hasn't come on yet. I have replaced the crank position sensor a couple times in the last year-year and half. Could it be that going out again or anyone have an idea if it could be another sensor? I don't currently own an OBD scan tool, probably should though. Have been borrowing one from a friend when needed. Did also replace the IAC valve about a year ago too.
I haven't pulled plugs to check them yet either, but I did replace coils, wires, and plugs about 15,000-20,000 miles ago.
Any ideas before I start blindly replacing sensors or just take it to my trusted mechanic (who is always swamped with work)? Or recommendations on which sensors you would start with?
Last edited by nitrousjunky; 12-07-2018 at 10:42 AM.
#2
CF Veteran
![Default](https://www.cherokeeforum.com/images/icons/icon1.gif)
A mixture problem that comes on after warm-up is most often associated with an O2 sensor that is no longer providing accurate values to the computer. O2 sensors are good for about 110k miles, so factor that into your troubleshooting.
If the low idle can be entirely corrected by depressing the gas pedal a little, that is also a sign of the IAC not properly managing the air flow. Unfortunately, this can also be the result of a CPS that is reporting strange RPM numbers to the computer (would suspect IAC first). One that is working when it is cold, but gets worse as it warms up.
If I was in your position, my first goal would be to get an OBD2 scanner on it so that I could see the RPM values and Long Term Fuel Trim values. If the RPM values appeared reasonable, I would not suspect the CPS involved. I would be looking for higher than normal Long Term Fuel Trim values (numbers greater than about 8% after the vehicle is warmed up), if I observed those higher numbers, O2 sensors would be next on my list to test. I would use the scanner to show me what the voltage on the O2 sensor was doing, I would be looking for a full range of numbers from .1 - .9 over time if one appeared to be stuck at a low number or high number all the time I would replace that O2 sensor.
If the low idle can be entirely corrected by depressing the gas pedal a little, that is also a sign of the IAC not properly managing the air flow. Unfortunately, this can also be the result of a CPS that is reporting strange RPM numbers to the computer (would suspect IAC first). One that is working when it is cold, but gets worse as it warms up.
If I was in your position, my first goal would be to get an OBD2 scanner on it so that I could see the RPM values and Long Term Fuel Trim values. If the RPM values appeared reasonable, I would not suspect the CPS involved. I would be looking for higher than normal Long Term Fuel Trim values (numbers greater than about 8% after the vehicle is warmed up), if I observed those higher numbers, O2 sensors would be next on my list to test. I would use the scanner to show me what the voltage on the O2 sensor was doing, I would be looking for a full range of numbers from .1 - .9 over time if one appeared to be stuck at a low number or high number all the time I would replace that O2 sensor.
#3
Junior Member
Thread Starter
Join Date: Sep 2012
Location: Brevard, NC
Posts: 49
Likes: 0
Received 0 Likes
on
0 Posts
Year: 2001
Model: Cherokee
Engine: 4.0
![Default](https://www.cherokeeforum.com/images/icons/icon1.gif)
Thanks, that's exactly the kind of info I was looking for. I was suspecting possibly the O2 sensors or the IAC possibly again. I picked up the IAC from the same source as the first CPS I changed out, that cps lasted about a month.
Just purchased an OBD2 scanner and have that on the way. Between this XJ and my 96 4 runner, I'll get good use out of it.
Are parts house (Bosch, etc..) O2 sensors decent for the XJs ? It may be the original O2 sensors in it.
Just purchased an OBD2 scanner and have that on the way. Between this XJ and my 96 4 runner, I'll get good use out of it.
Are parts house (Bosch, etc..) O2 sensors decent for the XJs ? It may be the original O2 sensors in it.
#4
Newbie
Join Date: Nov 2018
Location: London. Ohio, USA
Posts: 23
Likes: 0
Received 0 Likes
on
0 Posts
Year: 2000
Model: Cherokee (XJ)
Engine: 4.0L I6
![Default](https://www.cherokeeforum.com/images/icons/icon1.gif)
Thanks, that's exactly the kind of info I was looking for. I was suspecting possibly the O2 sensors or the IAC possibly again. I picked up the IAC from the same source as the first CPS I changed out, that cps lasted about a month.
Just purchased an OBD2 scanner and have that on the way. Between this XJ and my 96 4 runner, I'll get good use out of it.
Are parts house (Bosch, etc..) O2 sensors decent for the XJs ? It may be the original O2 sensors in it.
Just purchased an OBD2 scanner and have that on the way. Between this XJ and my 96 4 runner, I'll get good use out of it.
Are parts house (Bosch, etc..) O2 sensors decent for the XJs ? It may be the original O2 sensors in it.
#6
Junior Member
Join Date: Feb 2018
Posts: 68
Likes: 0
Received 0 Likes
on
0 Posts
Model: Cherokee(XJ)
Engine: 4.0L I6
![Default](https://www.cherokeeforum.com/images/icons/icon1.gif)
I highly recommend BlueDriver. I have diagnosed a bad upstream O2S, downstream O2S, MAP sensor, IAC, and found a bad coil wire using the STFT and LTFT real-time monitoring and available real-time data.
If the fuel trims are crazy rich (highly negative) it could be causing the stall - a good upstream O2S will cause the engine to go into closed loop in about 30 secs. When the engine first starts, it operates in open loop, default programming and is typically around -7 to -5% on the LTFT and 0% on the STFT.
If the heater is bad on the O2S, it can't properly measure O2 in your exhaust. In this case, your O2S voltage should be low on the sensor, reporting a lot of fuel in the exhaust gas and therefore trying to further make the FT negative, backing off the pulse width of the injectors.
I would also check the reading on your coolant temperature sensor, and intake air temp, as this can screw-up how the vehicle is maintaining the pulse width and how the ECU is entering into closed loop.
Last edited by jburg318; 12-08-2018 at 08:33 AM.
#7
CF Veteran
Join Date: Nov 2010
Location: In the middle of Minnesota!
Posts: 5,812
Received 104 Likes
on
92 Posts
Year: 1999
Model: Cherokee
Engine: 4.0
![Default](https://www.cherokeeforum.com/images/icons/icon1.gif)
Absolutely go with NTK oxygen sensors; they are the original equipment mfg. for the oxygen sensors on your 2001.
I really do like most Bosch products and while Bosch oxygen sensors work fine for the early Renix XJ 87-90 as they were OEM at that time, from 91-01 it's been NTK.
Not that expensive and widely available. Go NTK.
I really do like most Bosch products and while Bosch oxygen sensors work fine for the early Renix XJ 87-90 as they were OEM at that time, from 91-01 it's been NTK.
Not that expensive and widely available. Go NTK.
Last edited by tjwalker; 12-07-2018 at 05:54 PM.
Trending Topics
#8
Junior Member
Thread Starter
Join Date: Sep 2012
Location: Brevard, NC
Posts: 49
Likes: 0
Received 0 Likes
on
0 Posts
Year: 2001
Model: Cherokee
Engine: 4.0
![Default](https://www.cherokeeforum.com/images/icons/icon1.gif)
Thanks guys!! I had researched a bit and saw a few others saying NTK on the O2s as well.
We'll see what the real time data shows when the OBD2 gets here.
We'll see what the real time data shows when the OBD2 gets here.
#9
Newbie
Join Date: Nov 2018
Location: London. Ohio, USA
Posts: 23
Likes: 0
Received 0 Likes
on
0 Posts
Year: 2000
Model: Cherokee (XJ)
Engine: 4.0L I6
![Default](https://www.cherokeeforum.com/images/icons/icon1.gif)
NTK from factory? Wow! Mine must have been replaced in the past then lol. A lot of things on mine were factory, and incredibly worn out and never replaced. Can't go wrong either way, NTK or Bosch.
#10
Junior Member
Thread Starter
Join Date: Sep 2012
Location: Brevard, NC
Posts: 49
Likes: 0
Received 0 Likes
on
0 Posts
Year: 2001
Model: Cherokee
Engine: 4.0
![Default](https://www.cherokeeforum.com/images/icons/icon1.gif)
Alright update time.
Finally got my OBD2 scanner, long story (horrible ebay seller). In the mean time I picked up a Mopar CPS and swapped that out. Definitely wasn't the CPS.
Just sat in the Jeep and let it idle for about 25 minutes while monitoring. Here's what I saw in that period letting it idle-
Long Term Fuel Trim - Bank 1 was 3.1-3.9% and Bank 2 was staying around -1.6%
All 4 O2 sensors were fluctuating between .1-.8
Coolant temp got up to 205 degrees and intake temp got up to 145 degrees.
Idled fine the entire 25 minutes, I shifted the Jeep into Drive and it stalled out.
Only had one pending code, a misfire on cylinder 1.
I may monitor it again on the drive home this evening, but I'm thinking the next step is ordering the Mopar Idle Air Control Motor. Unless someone suggest otherwise.
Finally got my OBD2 scanner, long story (horrible ebay seller). In the mean time I picked up a Mopar CPS and swapped that out. Definitely wasn't the CPS.
Just sat in the Jeep and let it idle for about 25 minutes while monitoring. Here's what I saw in that period letting it idle-
Long Term Fuel Trim - Bank 1 was 3.1-3.9% and Bank 2 was staying around -1.6%
All 4 O2 sensors were fluctuating between .1-.8
Coolant temp got up to 205 degrees and intake temp got up to 145 degrees.
Idled fine the entire 25 minutes, I shifted the Jeep into Drive and it stalled out.
Only had one pending code, a misfire on cylinder 1.
I may monitor it again on the drive home this evening, but I'm thinking the next step is ordering the Mopar Idle Air Control Motor. Unless someone suggest otherwise.
#11
Junior Member
Thread Starter
Join Date: Sep 2012
Location: Brevard, NC
Posts: 49
Likes: 0
Received 0 Likes
on
0 Posts
Year: 2001
Model: Cherokee
Engine: 4.0
![Default](https://www.cherokeeforum.com/images/icons/icon1.gif)
Second update-
Checked it again when I got home and noticed something off.
On the Short term fuel trim, B1S1 and B2S1 were 1.6% and -.8-1.0
B1S2 and B2S2 were both holding steady at 99.2%
Checked it again when I got home and noticed something off.
On the Short term fuel trim, B1S1 and B2S1 were 1.6% and -.8-1.0
B1S2 and B2S2 were both holding steady at 99.2%
#12
CF Veteran
![Default](https://www.cherokeeforum.com/images/icons/icon1.gif)
Those initial idle numbers you posted definitely were reasonable. I can't quite make sense of your follow up numbers. But the B1S1 and B2S1 being at short term 1.6% is reasonable.
I re-read your initial post. So, if I understand correctly, the problem does not present itself until you shift into gear (any gear other than Park or Neutral I would assume). An engine that goes very low rpm and/or stalls when slowing down at stop signs, or that stalls when shifting into a gear other than P or N can also be caused by a torque converter lock-up clutch that is not properly disengaging. So that instead of the engine free-wheeling at idle with your foot on the brake (while in gear), the motor is trying to turn the transmission (which isn't moving because you are stopped or slowing down), so the transmission drags the motor down with it until it stalls.
It can be caused by a variety of things. A failing torque converter lockup clutch solenoid (one of the 3 shift solenoids in your transmission). Or a failing brake pedal switch (are your brake lights working properly?). Or a failing speed sensor on the transmission.
Next time you can scan while driving see what the scanner is reporting for speed and engine rpm. See if anything looks unusual. Also it should be able to present throttle position (as a percentage) take not of that value at idle, and while driving. It should be higher while driving, and then reduce back down to the idle value when your foot is off the pedal. On my 96 the idle throttle position value is about 16.9% though let's not assume that the 2001 would be the same.
I re-read your initial post. So, if I understand correctly, the problem does not present itself until you shift into gear (any gear other than Park or Neutral I would assume). An engine that goes very low rpm and/or stalls when slowing down at stop signs, or that stalls when shifting into a gear other than P or N can also be caused by a torque converter lock-up clutch that is not properly disengaging. So that instead of the engine free-wheeling at idle with your foot on the brake (while in gear), the motor is trying to turn the transmission (which isn't moving because you are stopped or slowing down), so the transmission drags the motor down with it until it stalls.
It can be caused by a variety of things. A failing torque converter lockup clutch solenoid (one of the 3 shift solenoids in your transmission). Or a failing brake pedal switch (are your brake lights working properly?). Or a failing speed sensor on the transmission.
Next time you can scan while driving see what the scanner is reporting for speed and engine rpm. See if anything looks unusual. Also it should be able to present throttle position (as a percentage) take not of that value at idle, and while driving. It should be higher while driving, and then reduce back down to the idle value when your foot is off the pedal. On my 96 the idle throttle position value is about 16.9% though let's not assume that the 2001 would be the same.
#13
Junior Member
Thread Starter
Join Date: Sep 2012
Location: Brevard, NC
Posts: 49
Likes: 0
Received 0 Likes
on
0 Posts
Year: 2001
Model: Cherokee
Engine: 4.0
![Default](https://www.cherokeeforum.com/images/icons/icon1.gif)
If it were the transmission or torque converter, wouldn’t the idle correct itself once shifted back into park or neutral?
Once it starts the issue after being warm, shifting into park doesn’t regulate the idle. It will stall out in park unless you feather the gas pedal. After it stalls out, I can crank it again and it still won’t idle in park.
A few mornings i’ve started The Jeep early for it to warm up and defrost the windshield. If I do this, the weak idle issue is present at the stop sign (just down the street from my driveway). If I don’t start it early, I can stop at that sign and multiple red lights in the first 5 minutes of the drive with no issue. Those days it is only noticeable when I pull into my parking place at work (which is about a 15 minute drive).
Could the weird short term fuel numbers on those mean that both downstream O2 sensors are bad (assuming those trims represents the second/downstream sensors) or possibly clogged cats?
Once it starts the issue after being warm, shifting into park doesn’t regulate the idle. It will stall out in park unless you feather the gas pedal. After it stalls out, I can crank it again and it still won’t idle in park.
A few mornings i’ve started The Jeep early for it to warm up and defrost the windshield. If I do this, the weak idle issue is present at the stop sign (just down the street from my driveway). If I don’t start it early, I can stop at that sign and multiple red lights in the first 5 minutes of the drive with no issue. Those days it is only noticeable when I pull into my parking place at work (which is about a 15 minute drive).
Could the weird short term fuel numbers on those mean that both downstream O2 sensors are bad (assuming those trims represents the second/downstream sensors) or possibly clogged cats?
Last edited by nitrousjunky; 01-11-2019 at 09:38 PM.
#14
CF Veteran
![Default](https://www.cherokeeforum.com/images/icons/icon1.gif)
If it were the transmission or torque converter, wouldn’t the idle correct itself once shifted back into park or neutral?
Once it starts the issue after being warm, shifting into park doesn’t regulate the idle. It will stall out in park unless you feather the gas pedal. After it stalls out, I can crank it again and it still won’t idle in park.
A few mornings i’ve started The Jeep early for it to warm up a defrost the windshield. If I do this, the weak idle issue is present at the stop sign (just down the street from my driveway). If I don’t start it early, I can stop at that sign and multiple red lights in the first 5 minutes of the drive with no issue. Those days it is only noticeable when I pull into my parking place at work.
Could the weird short term fuel numbers on those mean that both downstream O2 sensors are bad (assuming those trims represents the second/downstream sensors) or possibly clogged cats?
Once it starts the issue after being warm, shifting into park doesn’t regulate the idle. It will stall out in park unless you feather the gas pedal. After it stalls out, I can crank it again and it still won’t idle in park.
A few mornings i’ve started The Jeep early for it to warm up a defrost the windshield. If I do this, the weak idle issue is present at the stop sign (just down the street from my driveway). If I don’t start it early, I can stop at that sign and multiple red lights in the first 5 minutes of the drive with no issue. Those days it is only noticeable when I pull into my parking place at work.
Could the weird short term fuel numbers on those mean that both downstream O2 sensors are bad (assuming those trims represents the second/downstream sensors) or possibly clogged cats?
2. Perhaps, but downstream sensors usually just measure cat efficiency and are not involved in the mixture adjustment process. But different years might handle this differently, so I don't want to assume. About clogged cats...perhaps but they would be clogged from the time the vehicle is started. So not sure that adds up either.
#15
Junior Member
Thread Starter
Join Date: Sep 2012
Location: Brevard, NC
Posts: 49
Likes: 0
Received 0 Likes
on
0 Posts
Year: 2001
Model: Cherokee
Engine: 4.0
![Default](https://www.cherokeeforum.com/images/icons/icon1.gif)
I thought that was the case with the downstream O2s, but wasn’t positive.
Valid point on the clogged cats should be constant.
I’m trying to decide whether to get the IAC next or...?
Valid point on the clogged cats should be constant.
I’m trying to decide whether to get the IAC next or...?