Rough Idle in Gear and Faulty Misfire Codes

tjsahara

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Mar 21, 2023
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Hello TJ Forum,

I have been trouble shooting my 01 TJ with 59k miles for the last year or so and cannot seem to find the cause of its issues.
The Jeep has an idle around 500rpm and once put into gear there is an immediate difference in the vibration at stand still; the vibration goes away once the throttle is engaged after 1mph or so. This rough idling in gear is also significantly worse in 4H at stand still. The idle issue is paired with misfire codes that have been diagnosed at multiple shops resulting in the coil pack, spark plugs, o2 sensors replaced, throttle body removed and cleaned, IAC sensor removed and cleaned, and a fuel injector cleaner. All replacement parts used were NGK/NTK/Name brand parts. I have never felt a misfire while driving the Jeep and two shops have gone as far to say there are no misfires present in the cylinders. A year ago I removed the stock suspension and replaced it with a 3.5” Metalcloak lift with a Tom Wood’s Rear Drive shaft and Teraflex Slip Yoke Eliminator; may this link to any of the Jeep’s vibration symptoms?

Do y’all have any advice on the rough idle in gear at stand still and the possibility of a “faulty” misfire code? Other than the rough idle in gear and the misfire codes coming on and off throughout the year, the Jeep drives and runs great. She’s in beautiful condition and I’d like to ensure my future children and grandkids can drive it around one day. Thanks for any help and please do not hesitate to ask for more info if needed!!
 
So long as your spark plugs are not a single-tipped Platinum like the Autolite AP985 or Champion 3034 which will cause bad idles/misfires, I'd suspect a bad crankshaft position sensor. If you decide to replace it try to find a Mopar or at least a premium replacement like NAPA's best. Avoid store brand sensors like Duralast from AutoZone.
 
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I got random misfire codes for months...changed every other sensor looking for a Mopar CPS and finally pulled the trigger on a Napa Echlin. No more misfires.

-Mac
 
So long as your spark plugs are not a single-tipped Platinum like the Autolite AP985 or Champion 3034 which will cause bad idles/misfires, I'd suspect a bad crankshaft position sensor. If you decide to replace it try to find a Mopar or at least a premium replacement like NAPA's best. Avoid store brand sensors like Duralast from AutoZone.

Thank you for the response Jerry. Does this part fit my 01 Sahara “Mopar 4897321AA Crankshaft Position Sensor”? Looks to be the correct part, just want to ensure before ordering.
 
I got random misfire codes for months...changed every other sensor looking for a Mopar CPS and finally pulled the trigger on a Napa Echlin. No more misfires.

-Mac

Thanks for the response! We’re you looking for the “Mopar 4897321AA Crankshaft Position Sensor”?
 
Thank you for the response Jerry. Does this part fit my 01 Sahara “Mopar 4897321AA Crankshaft Position Sensor”? Looks to be the correct part, just want to ensure before ordering.
I don't have my Mopar parts guide here, just make sure it's for your automatic transmission. There's another one made for a manual transmission that won't work.
 
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My experience with a bad CPS is that the (2000 TJ) will suddenly turn off the engine while driving.
QUESTION: Would a bad Crankshaft Position Sensor also cause a P0301and very rough idle?
 
Just for clarity:

CKPS/CKS = crank position sensor
CPS = cam position sensor

Last I checked, the mopar CKPS (auto) was still available, but not the CPS

Note: I've also had good luck with a Napa Echlin CPS
 
Just for clarity:

CKPS/CKS = crank position sensor
CPS = cam position sensor

Last I checked, the mopar CKPS (auto) was still available, but not the CPS

Note: I've also had good luck with a Napa Echlin CPS

Thank you. I found what what was sold as an OEM ckps and labeled as one, but still have my doubts. I'll install it along with
new plugs and pray. Would bad O2 sensors cause a misfire and very rough idle while in gear as well?
 
Would bad O2 sensors cause a misfire and very rough idle while in gear as well?
Yes a bad upstream O2 sensor can, your 2000 has two upstream and two downstream O2 sensors. The worst I ever experienced with a bad upstream O2 sensor was a Toyota I used to own. When its upstream O2 sensor failed it would literally barely idle or run, I didn't think I was going to make it home the night before I changed the O2 sensor. It ran beautifully after replacing it.

If you decide to replace your O2 sensors make sure to ONLY install NTK, NGK, or Mopar... all of those having been manufactured by NTK. Avoid store-brand O2 sensors and especially avoid Bosch O2 sensors in a Jeep, they don't work properly in a Jeep for some reason.
 
Thanks so much, Jerry. I had a shop (Midas I think) replace them like 6 months ago. I had NGK replacements and they refused to install them. They insisted they install their own parts. This could be my problem! I appreciate your help! I'll post here with results ASAP.
 
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So I installed 6 new plugs this weekend. Autolite Iridium XP985. The old ones were the Bosch, so I thought for sure that was my problem. NOPE. It now idles worse than before. Next I will install another NGK coil pack. (So hard to know if they are fake). If that doesn't work, I will install another "MOPAR" Crankshaft Position Sensor. From Rock Auto. If that doesn't work, Rock Auto has "MOPAR" top end O2 sensors. They are $115 each. If that doesn't work, I won't know what to do. I just had the head pulled, leak tested, new valve job, new valves, new guides, new springs, EVERYTHING. SO frustrating!
 
So I installed 6 new plugs this weekend. Autolite Iridium XP985. The old ones were the Bosch, so I thought for sure that was my problem. NOPE. It now idles worse than before. Next I will install another NGK coil pack. (So hard to know if they are fake). If that doesn't work, I will install another "MOPAR" Crankshaft Position Sensor. From Rock Auto. If that doesn't work, Rock Auto has "MOPAR" top end O2 sensors. They are $115 each. If that doesn't work, I won't know what to do. I just had the head pulled, leak tested, new valve job, new valves, new guides, new springs, EVERYTHING. SO frustrating!

Do not punish yourself by overpaying for o2 sensors. That's a mistake.

Last I read, you didn't know the brand of your o2 sensors. You want that information —> and change the parts if the wrong parts are installed. I don't care how much you paid a shop to install those parts. The result is the only thing that matters, so you want to verify what you have installed.

Never assume the current step will fix your issue. Curbing your expectations will help prevent you from becoming an emotional ballistic missile when it doesn't fix it. Instead, use those moments to focus and energize yourself into tackling the next step.

FWIW, I recently replaced my fouled NGK o2 sensors with new NGK o2 sensors (AMAZON —> $120 total).

All you need is a 22mm or 7/8" wrench and about 45 minutes of your time. Yours haven't been on there long, so you should be able to crack them right off.

Below should be the list of plugs for your rig (according to the o2 thread I pulled up). I would verify on RA but purchase on Amazon.

Screen Shot 2023-03-27 at 1.46.52 AM.png


Hang in there. You'll get it.
 
Last edited:
Do not punish yourself by overpaying for o2 sensors. That's a mistake.

Last I read, you didn't know the brand of your o2 sensors. You want that information —> and change the parts if the wrong parts are installed. I don't care how much you paid a shop to install those parts. The result is the only thing that matters, so you want to verify what you have installed.

Never assume the current step will fix your issue. Curbing your expectations will help prevent you from becoming an emotional ballistic missile when it doesn't fix it. Instead, use those moments to focus and energize yourself into tackling the next step.

FWIW, I recently replaced my fouled NGK o2 sensors with new NGK o2 sensors (AMAZON —> $120 total).

All you need is a 22mm or 7/8" wrench and about 45 minutes of your time. Yours haven't been on there long, so you should be able to crack them right off.

Below should be the list of plugs for your rig (according to the o2 thread I pulled up). I would verify on RA but purchase on Amazon.

View attachment 410771

Hang in there. You'll get it.

I just purchased an 01 with the 6 cylinder and have the same issue on the shake when at a stop and smooth when going down the road. I do have the two codes that came up and both codes are for the banks 1 & 2 downstream 02 sensors, Would these sensors cause these symptoms as well?
 
I just purchased an 01 with the 6 cylinder and have the same issue on the shake when at a stop and smooth when going down the road. I do have the two codes that came up and both codes are for the banks 1 & 2 downstream 02 sensors, Would these sensors cause these symptoms as well?

Easy part of this is that the computer is telling u both sensors are bad, and they are a cheap fix. Hard to know if it will solve your issue, but it doesn’t make sense to start anywhere else.

84A09091-7098-4759-BF40-A2E722D2C387.jpeg


Link: https://wranglertjforum.com/threads/the-official-jeep-wrangler-tj-oxygen-o2-sensor-thread.4068/
 
I got random misfire codes for months...changed every other sensor looking for a Mopar CPS and finally pulled the trigger on a Napa Echlin. No more misfires.

-Mac

Ditto, my misfire was not causing a rough idle. It would just throw a misfire code sometimes 4 sometimes 6 very random. Jeep ran fine. Replaced with Napa Echlin as well this weekend took it for a long drive and no more codes.

Thanks Mac and Jerry B for the suggestion.
 
So I installed 6 new plugs this weekend. Autolite Iridium XP985. The old ones were the Bosch, so I thought for sure that was my problem. NOPE. It now idles worse than before. Next I will install another NGK coil pack. (So hard to know if they are fake). If that doesn't work, I will install another "MOPAR" Crankshaft Position Sensor. From Rock Auto. If that doesn't work, Rock Auto has "MOPAR" top end O2 sensors. They are $115 each. If that doesn't work, I won't know what to do. I just had the head pulled, leak tested, new valve job, new valves, new guides, new springs, EVERYTHING. SO frustrating!

I feel your frustration. Please keep us posted on your efforts!
 
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Ditto, my misfire was not causing a rough idle. It would just throw a misfire code sometimes 4 sometimes 6 very random. Jeep ran fine. Replaced with Napa Echlin as well this weekend took it for a long drive and no more codes.

Thanks Mac and Jerry B for the suggestion.

It's wild you got so many codes. Mine only popped a CPS code and cut power. (also have had good luck with the Napa Echlin CPS)