Suddenly intermittently stumbling while accelerating, idling fine

[Mogul345]

Well, my wrangler (98 4.0 Auto) is the latest car to be angry with me. Drove it for the first time this week. Sat idling for about 5 min before I left the house. About 2 blocks away from the house, all of a sudden while accelerating reasonably lightly from a stop, started stumbling and seemingly misfiring and definitely not accelerating. Pulled over, idled like a kitten. So I pressed on to my destination. Kept stumbling seemingly usually over 2k. And if I stomped on it, instant stumbling/misfiring. But if I was easy on it, it would accelerate just fine up to about 2k. Kept pressing on to my destination (about a mile away, in like 25mph traffic). Got up fully to temp by the time I left the destination, as I left it running while at the destination for like 5-10min max.

On the way home, she ran seeming great, stomped on it a bunch of times, accelerated just fine. But then a couple of blocks from home, stumbled again, and even idled kinda rough for a few seconds.

I pulled the throttle body, and cleaned it and the IAC valve with throttle body cleaner a little over a month ago. I did this because some threads here indicated that it might be the cause of my intermittently stupidly high idle that would happen randomly when putting it in park, or on random start. I was very careful to make a new gasket for the IAC housing, and used a torque wrench to tighten everything down. I changed the plugs (NGK copper)/wires (NGK)/cap/rotor a week later, and I double checked the gap with my feeler gauge before installation. Both of these were done over a month ago and it's run great for this past month.

No check engine light, so I don't think there should be any codes. But am about to go outside with my BT OBD2 sender and the Torque app to see if there's anything interesting.

Anyone have any ideas where I should start looking?

EDIT: Well, I pulled the codes, and of course, there was a single code - P0351: Ignition coil "A" Primary/Secondary Circuit. Guess maybe I've got an intermittently failing ignition coil?

I love when there's codes that dont trip the CEL...

 

[Steel City 06]

Could be a failing catalytic converter. Often a chunk breaks free and flops around, sometimes clogging the flow path and causing a fairly severe misfire at higher loads, but sometimes still flowing enough to idle okay.

 

[Mogul345]

Once I pulled the codes, I searched the forum for the code and found this thread. It sounds similar, but since I've got a 1998 I've got a coil and distributor, not coil packs. Is there a similar test procedure for the older ignition setup? The FSM for 1998 only seems to talk about testing coil resistance.

 

[JKP]

Weak coil. High RPM, high load snuffs the spark. It will keep getting worse.

Only current production coil that worked long term on my YJ was the Standard Ign Blue Streak. Mopar, MSD, etc, all China made, lasted anywhere from 3 months to 2 yrs, but all failed. Blue Streak is still working at 5 yrs or so.

 

[Mogul345]

Weak coil. High RPM, high load snuffs the spark. It will keep getting worse.

Only current production coil that worked long term on my YJ was the Standard Ign Blue Streak. Mopar, MSD, etc, all China made, lasted anywhere from 3 months to 2 yrs, but all failed. Blue Streak is still working at 5 yrs or so.

Got it. OK so just toss a new coil into it then. Will look for the Blue Streak.

EDIT - Nice, way cheaper than the Mopar one too.

 

[JKP]

If you're not in a hurry, RockAuto will have the best price.

 

[Mogul345]

Yup, RockAuto wins as always, and the TODO list of Jeep jobs continues to grow lol

 

[Staid]

Well, my wrangler (98 4.0 Auto) is the latest car to be angry with me. Drove it for the first time this week. Sat idling for about 5 min before I left the house. About 2 blocks away from the house, all of a sudden while accelerating reasonably lightly from a stop, started stumbling and seemingly misfiring and definitely not accelerating. Pulled over, idled like a kitten. So I pressed on to my destination. Kept stumbling seemingly usually over 2k. And if I stomped on it, instant stumbling/misfiring. But if I was easy on it, it would accelerate just fine up to about 2k. Kept pressing on to my destination (about a mile away, in like 25mph traffic). Got up fully to temp by the time I left the destination, as I left it running while at the destination for like 5-10min max.

On the way home, she ran seeming great, stomped on it a bunch of times, accelerated just fine. But then a couple of blocks from home, stumbled again, and even idled kinda rough for a few seconds.

I pulled the throttle body, and cleaned it and the IAC valve with throttle body cleaner a little over a month ago. I did this because some threads here indicated that it might be the cause of my intermittently stupidly high idle that would happen randomly when putting it in park, or on random start. I was very careful to make a new gasket for the IAC housing, and used a torque wrench to tighten everything down. I changed the plugs (NGK copper)/wires (NGK)/cap/rotor a week later, and I double checked the gap with my feeler gauge before installation. Both of these were done over a month ago and it's run great for this past month.

No check engine light, so I don't think there should be any codes. But am about to go outside with my BT OBD2 sender and the Torque app to see if there's anything interesting.

Anyone have any ideas where I should start looking?

EDIT: Well, I pulled the codes, and of course, there was a single code - P0351: Ignition coil "A" Primary/Secondary Circuit. Guess maybe I've got an intermittently failing ignition coil?

I love when there's codes that dont trip the CEL...

Hi there. Ive got a 2005 TJ, engine warning light was always on and the car would choke at 3k revs. Went round the houses, spark plugs, unit, oxygen sensor etc. Came down to a simple earth lead - flat, metal, silver ribbon close to the centre on the engine side of the dash. Was loose, not grounded, likely from the previous owner. Attached it, engine light off and no more choking. It could be something simple like that so worth a check. Good luck!

 

[Mogul345]

Update - problem still exists. I replaced the coil yesterday with a Blue Streak one per recommendation above. But still is throwing code.

Right before the coil was installed it was the worst it's ever been. It would not run. Just sputtering and death. Right after I installed the coil, it also did the stumbling and dying, though it ran for a bit. I waited maybe 30 minutes. Then I proceeded to clear the code in the PCM, drive it a couple of miles around my neighborhood just fine. Fuel trims, timing advance all seemingly looked OK from OBD via the Torque app.

But today went and drove it. Started fine cold, got about a mile, and then it all started again. Died in a parking garage as I got to the destination. Was able to get it restarted after a couple of tries, and get it home. It was unhappy the whole way home, but by the time I parked it, it was running pretty good, with the occasional stumble. But the same ignition code is back.

I checked all the grounds in the engine bay, they seem tight (except the strap that connects the hood to the firewall, but that seems like it wouldn't be involved.

What's the next thing to look at? Otherwise I think it's time to give up and take it to a shop.