97 XJ 4.0 AW4 - Stutter / Misfire - I know I know but I've tried so many things.

Hey All!

This seems to be a common issue but I’ve read up a bunch on this and none of the fixes have worked for me so here goes!

1997 Jeep XJ - 4.0L AW4 - 190,000 miles

I’ve had a real bad stutter that feels like the Jeep is misfiring when idling. I have also had a few issues with the stutter/ miss while on the highway at about 65mph. Feels like it misses and stutters for a second or two and then runs fine afterward. The Tach drops about 50-100 RPM when it misses on idle. It’s not a drastic drop and when it is not stuttering it runs pretty smooth for a 4.0 with 190,000 miles.

It starts right up every-time and will cruise on the freeway at 70 no problem but the stutter at idle is real bad cold or hot. Shakes the whole jeep.

This has been giving me trouble for a few weeks now and I have done quite a bit to remedy the situation, all to no avail!

Here's what I have done so far.

- Oil Change w/ new filter
- New Distributor Cap / Wires / Plugs
- Battery - The jeep starts right up and has no issues electrically so I can’t imagine the battery is bad…
- Searched for Vacuum Leaks. (Can’t find any obvious leaks, could a small l leak really cause such big issues?)
- Cleaned Throttle Body
- New Air Filter
- New IAC
- New TPS Sensor
- New Map Sensor
- Sea Foam Treatment in Gas Tank (I’m on my second tank of gas with this issue so it’s probably not bad gas)
- Sea Foam down the throttle body treatment
- New Upstream 02 Sensor
- New CPS Sensor (Genuine Mopar Part)
- New 4 Hole Injectors
- Fuel Rail checked for leaks and cleaned
- Fuel Pump Pressure checked - stays at 50psi as it should. (Should I drop the tank and check the pump / filter? It seems to be working as it should so I was not planning to do this)
- New MSD Coil swapped in from my other XJ just to be sure it wasn’t the coil.
- Electrical Ground connections cleaned up and checked
- Pulled the downstream 02 Sensor from the cat and ran the jeep to see if the cat was clogged. Ran basically the same but a little louder. Figure the cat is probably not clogged? Hard for me to tell here… Any better ways to check this?


I’ve got a new temp sensor coming today and will be switching that out.

I think that is it! Basically I’ve got the Jeep running great when it’s not missing and stuttering.

If there is anything you guys can think of, it would help a ton. I’m basically pulling my hair out at this point.


Thank you,
Zach

Is or was the check engine light ON ? Have you cheeked for any pending trouble codes ?

Have you checked for damaged valves and/or failed valve springs ?

When the distributor was installed, was the base timing set correctly, and the Cam Sensor synchronization checked with a DRB-III Scan Tool ?

Are you installing NGK/NTK O2 sensors, and not Bosch, or the cheap Chinese junk from the auto parts store ?

Are you installing genuine Jeep OBD engine sensors ? Most auto parts stores sell cheap crappy Chinese made parts, some that even come with a " Lifetime Warranty". These parts are poorly manufactured and/or made from inferior materials. They are often out of specification, or even failed, right out of the box. The ones that are not faulty many times will have a short service life before they fail. Always buy top quality replacement parts and genuine Jeep engine sensors. Numerous threads detail long and frustrating searches for a "problem" that ended up being cured simply with genuine Jeep repair parts. Cheap parts are cheap for a reason.