Finally Fixed My 1998 Jeep Wrangler 4.0 Automatic Stumble Issue – Here’s What Worked

[TJGreenhorn]

TL;DR:
1998 Jeep Wrangler 4.0L automatic was stumbling. Tried spark plugs, wires, coil, distributor, CPS, O2 sensor, vacuum checks, throttle body, IAC, injectors, PCM—nothing worked.
Final fix: replaced distributor and used the original Cam Position Sensor from the old distributor. Jeep runs perfectly now.

After months of frustration, I finally resolved a stumble/surging problem on my 1998 Jeep Wrangler 4.0L automatic. Since I didn’t see this documented anywhere, I wanted to share my experience and what ultimately fixed it. Disclaimer: I’m by no means a “car guy,” but I consider myself an avid DIYer. I really enjoyed getting hands-on with the engine and figuring this out. Part of the reason that I bought this jeep was to get some hands-on experience with a car. Happy to be a part of the club now!

Symptoms:

• Jeep stumbled especially while driving, sometimes at idle. Started slow and got worse over a few weeks. Occasionally stalling due to the misfires.
• Rough idling; occasional stalls.
• Restarting temporarily “fixed” it.
• Inconsistent CEL codes: CPS codes, O2 codes, ASD/fuel pump relay codes.

What I Tried (in order):

1. Spark plugs, wires, distributor cap & rotor, ignition coil – standard tune-up. Did not fix the stumble.
2. Crankshaft Position Sensor (CPS) – replaced multiple times with NGK; misaligned CPS made Jeep run worse temporarily. (CPS was installed as high up as possible, versus flush. Yes I had the paper spacer on it, didnt seem to make a difference)
3. O2 Sensor Replacement – no effect.
4. Vacuum Leak Check – found throttle body leak; replaced throttle body.
5. IAC Valve Cleaning – no effect.
6. Big 7-WireKit – checked for grounding issues; no effect. (Bought this after checking grounds, even though they all checked out)
7. Alternator (replaced this due to a very infrequent odd multimeter reading, figured at 170K miles, it might be time to just do it anyways).
8. PCM Sent Out for Testing – PCM checked out fine; returned.
9. Fuel Injectors – replaced all; cylinder 3 slightly under ohmed. Fuel pressure fine.
10. Water Pump, Thermostat Housing, Thermostat – replaced while working in the engine because of leaks.

Breakthrough:

• Mechanic friend suggested removing the distributor.
• Distributor shaft had abnormal play → rotor skipped over cap contacts → Jeep stumbled.
• Replaced distributor (Extreme Terrain). Jeep ran better but still stumbled above ~2,000 RPM.

Final Fix:

• New distributor had an aftermarket Cam Position Sensor (CMP).
• Swapped in CMP from original distributor.
• Jeep now runs perfectly under all conditions—smooth idling, no stumbling, no surging.

Key Takeaways:

• Critical timing components (distributor + CMP) may fail mechanically or be sensitive to aftermarket parts.
• Stumbles/surging can point to mechanical issues in the distributor shaft, not just sensors or wiring.
• Sometimes OEM/original sensors are more reliable for Wranglers than aftermarket replacements.

Hopefully this helps someone else stuck in the endless cycle of replacing sensors, PCM, and injectors. This could save you a ton of time and frustration.

 

[Chris]

Thanks for sharing! This is bound to help someone in the future, I can guarantee it!

 

[hear]

What distributor did you go with? I replaced mine with a (go ahead and clutch your pearls) Duralast 3 years ago and have had zero issues.

 

[TJGreenhorn]

What distributor did you go with? I replaced mine with a (go ahead and clutch your pearls) Duralast 3 years ago and have had zero issues.

I went with this one off Extreme Terrain!
https://www.extremeterrain.com/jeep-wrangler-ignition-distributor-cap-rotor-apid106.html

 

[hear]

I went with this one off Extreme Terrain!
https://www.extremeterrain.com/jeep-wrangler-ignition-distributor-cap-rotor-apid106.html

I would not be surprised in the least to learn that yours is made in the same place mine way, and by some of the same people.

 

[lBasket]

by some of the same people.

Chinese children?

 

[hear]

Chinese children?

whoa whoa, let's low-say own-day on the acism-ray.

 

[macleanflood]

Here's big brother's (possibly sister...or them) response...

AI Mode

The classification of calling Chinese products "low quality" as racist is a subject of debate, with many viewing it as a stereotype with xenophobic or racist undertones, while others consider it a critique of product quality or an economic observation.
Arguments that it is racist/xenophobic

Sweeping Generalization: The primary argument is that the label is a sweeping generalization applied to all products from an entire nation, ignoring the reality that China produces a vast range of goods, from low-end items to high-end electronics and luxury goods for global brands like Apple.
Historical Precedent: The "cheap, low quality" reputation was previously applied to products from Japan and Taiwan, but changed as their economies developed and product specifications changed, suggesting the current stigma is a phase related to economic development, not an inherent national trait.
Consumer Choice/Western Demand: Many Chinese factories produce goods to the specifications requested by Western companies and consumers who prioritize low prices. The low quality often reflects the buyer's low budget, not a lack of manufacturing capability.
Association with Anti-Asian Sentiment: The stereotype can be linked to broader anti-Asian sentiment and media-driven attitudes that negatively frame the "Made in China" label, potentially influencing public opinion of the country and its people.

Arguments that it is not racist

Product Critique: Some argue that criticizing a product's quality is simply that—a product critique—and has nothing to do with race or ethnicity.
Country Equity/Brand Image: Others suggest that China has intentionally leveraged a "cheap but reliable" brand image as a competitive advantage in global markets. The negative perception is an unfortunate side effect of this economic strategy, not necessarily racism.
Economic Reality: A significant volume of low-cost, low-quality goods does flood the market, especially online marketplaces like Amazon. Some people view this as a simple observation of market reality, not a racial bias.

Ultimately, while the intent of an individual's comment may vary, the phrase relies on a broad, often inaccurate, stereotype about a large population and its capabilities, which can contribute to a climate of xenophobia or racism.

 

[ColoJeep]

Chinese children?

Sure , but nobody builds better lead based painted infant toys and generic ignition components ....

 

[hear]

Here's big brother's (possibly sister...or them) response...

AI Mode

The classification of calling Chinese products "low quality" as racist is a subject of debate, with many viewing it as a stereotype with xenophobic or racist undertones, while others consider it a critique of product quality or an economic observation.
Arguments that it is racist/xenophobic

Sweeping Generalization: The primary argument is that the label is a sweeping generalization applied to all products from an entire nation, ignoring the reality that China produces a vast range of goods, from low-end items to high-end electronics and luxury goods for global brands like Apple.
Historical Precedent: The "cheap, low quality" reputation was previously applied to products from Japan and Taiwan, but changed as their economies developed and product specifications changed, suggesting the current stigma is a phase related to economic development, not an inherent national trait.
Consumer Choice/Western Demand: Many Chinese factories produce goods to the specifications requested by Western companies and consumers who prioritize low prices. The low quality often reflects the buyer's low budget, not a lack of manufacturing capability.
Association with Anti-Asian Sentiment: The stereotype can be linked to broader anti-Asian sentiment and media-driven attitudes that negatively frame the "Made in China" label, potentially influencing public opinion of the country and its people.

Arguments that it is not racist

Product Critique: Some argue that criticizing a product's quality is simply that—a product critique—and has nothing to do with race or ethnicity.
Country Equity/Brand Image: Others suggest that China has intentionally leveraged a "cheap but reliable" brand image as a competitive advantage in global markets. The negative perception is an unfortunate side effect of this economic strategy, not necessarily racism.
Economic Reality: A significant volume of low-cost, low-quality goods does flood the market, especially online marketplaces like Amazon. Some people view this as a simple observation of market reality, not a racial bias.

Ultimately, while the intent of an individual's comment may vary, the phrase relies on a broad, often inaccurate, stereotype about a large population and its capabilities, which can contribute to a climate of xenophobia or racism.

Lol, I never said anything about ANY country. Ya'll are the ones ragging on our commie sweatshop workforce.

 

[macleanflood]

Sure , but nobody builds better lead based painted infant toys and generic ignition components ....

What about melamine infant formula and dog treats?

Unfortunately I think we get what we're paying for...

-Mac

 

[TheBoogieman]

Another crap Chinese product.

 

[hear]

What about melamine infant formula and dog treats?

Unfortunately I think we get what we're paying for...

-Mac

That's why my father-in-law feeds his dogs Jack Links jerky.


I wish I was kidding. When we go over to his house me & my boys raid "the dog food."

 

[lBasket]

That's why my father-in-law feeds his dogs Jack Links jerky.


I wish I was kidding. When we go over to his house me & my boys raid "the dog food."

I give my dog chicken jerky. No real reason a person couldn't eat it

 

[AndyG]

Thanks for sharing! This is bound to help someone in the future, I can guarantee it!

Thread like this are
pure gold

It would be cool if we could get a catalog of fixes-

 

[Chris]

I know damn well from playing guitar that the Chinese can build some exceptional stuff that in many cases is far better than a comparable American product (guitars in this case). However, you get what you pay for and the automotive market is flooded with cheap Chinese crap that lasts a few years at most. I guess they figure that most people don't keep their car past a few years so it doesn't matter.

It's unfortunate though, because there are folks (myself included) who are willing to pay premium for automatic replacement parts that will last a decade or more.

 

[ColoJeep]

I know damn well from playing guitar that the Chinese can build some exceptional stuff that in many cases is far better than a comparable American product (guitars in this case). However, you get what you pay for and the automotive market is flooded with cheap Chinese crap that lasts a few years at most. I guess they figure that most people don't keep their car past a few years so it doesn't matter.

It's unfortunate though, because there are folks (myself included) who are willing to pay premium for automatic replacement parts that will last a decade or more.

I feel it's even darker than that . It is the American companies that outsource and spec the parts to be made to a price point. Additionally , I don't trust the Chinese Communist government at all . They are playing the long game to screw us over .

 

[Chris]

I feel it's even darker than that . It is the American companies that outsource and spec the parts to be made to a price point. Additionally I don't trust the Chinese Communist government at all . They are playing the long game to screw us over .

Yes, they are playing the long game and nobody should trust the CCP. However, nobody should trust any government. All governments are crooked and corrupt. But American companies outsourcing the parts at a certain price point likely means that they have data on what people are willing to pay for a replacement part. My guess is that most people are too cheap to spend the sort of money it would take to get higher quality parts.

One more reason I'm happy that my Chevy has as few electronics as possible.

 

[ColoJeep]

Yes, they are playing the long game and nobody should trust the CCP. However, nobody should trust any government. All governments are crooked and corrupt. But American companies outsourcing the parts at a certain price point likely means that they have data on what people are willing to pay for a replacement part. My guess is that most people are too cheap to spend the sort of money it would take to get higher quality parts.

One more reason I'm happy that my Chevy has as few electronics as possible.

I totally agree that governments aren't to be trusted , but ultimately , these are spiritual issues , and go far beyond government . The price point issue is interesting , in some areas you have options , in some you don't . Your high end ChiCom guitar is a outlier , if it was only sourced through Autozone or Amazon it would be $ 69.95 and the quality would reflect the price point. I agree the K-10's lack of electronics is good ! , however even your manual trans conversion probably was many Chinese parts , (Clutch Hydraulics at minimum ) of varying quality . I hate that we only have a few options in the automotive world . I bought replacement disc pads made in India , because I couldn't go ChiCom. Just my opinion.

 

[Chris]

I totally agree that governments aren't to be trusted , but ultimately , these are spiritual issues , and go far beyond government . The price point issue is interesting , in some areas you have options , in some you don't . Your high end ChiCom guitar is a outlier , if it was only sourced through Autozone or Amazon it would be $ 69.95 and the quality would reflect the price point. I agree the K-10's lack of electronics is good ! , however even your manual trans conversion probably was many Chinese parts , (Clutch Hydraulics at minimum ) of varying quality . I hate that we only have a few options in the automotive world . I bought replacement disc pads made in India , because I couldn't go ChiCom. Just my opinion.

All you can do is try stuff out and see how long it lasts these days. We are the test dummies anymore. I have a habit of keeping spare parts on hand for those times where things decide to break.

Gone are the good old days where you could buy quality. Things will only continue to get worse as our civilization collapses all around us. You can already see it and this is just case in point. One of many examples!