lowend1

Greetings, all.
Intermittent drivability problem with our '93 XJ (2WD) 160k+ miles:
Periodically, unpredictably and almost always on the highway, the vehicle will exhibit sluggishness or poor throttle response. These are identifiable incidents, not general malaise. Almost feels like it is going to stall, but ultimately composes itself and soldiers on. There is also another sporadic issue where when slowing to a stop or shortly thereafter, the engine will stumble for a few seconds and then the idle speed increases and smooths out. Generally it starts fine, but it did mysteriously fail to do so on one occasion a few years back. I had it towed and when it got to the shop it started right up. I have had my mechanic run tests a couple of times and at this point it's usually cheaper to change parts than chase ghosts.
Things we have done over the past year:
Full tune up including coil
Replaced fuel filter
Cleaned throttle body
Replaced fuel pressure regulator
Replaced throttle position sensor
Replaced idle speed control motor
Replaced catalytic converter (was clogged), muffler and tailpipe
I'm thinking about changing the MAP sensor next, but I am admittedly guessing. Any additional ideas, brainstorms or Hail Marys are appreciated. Thanks!

gat

What is the fuel pressure at the rail in the following conditions? Sitting cold, key in on position, starting/cranking, running, 15 seconds - 5 minutes after killing the engine.
How powerful of a spark is being produce if any?
Try starting the vehicle with a teaspoon of gasoline poured straight into each combustion cylinder thru the spark plugs holes.

Try these things before further replacements. The fuel pressure regulator on older Jeep's when installed at the rail are not known for going bad ever. Some things like crankshaft position sensors are notorious, though.

lowend1

Thanks for the reply. I will have to test as you described.
The fuel pressure regulator was replaced because the nylon O-ring was split and leaking. The local parts store didn't have one separately so I bought the whole regulator. I stocked up on the O-ring when I found them online.

gat

Since you have a 1993, then you can check for any codes that have been thrown fairly easily. Is there a check engine light? If it was flashing, then that signifies a misfire.

Out of curiosity what was your tune up? I would consider replacing the air filter, fuel filter, spark plugs, spark plug wires, distributor cap, and distributor rotor a full "tune up". It is so easy to change all of these things on your and my 1992 that I like to do these things when I am having an issue because if regular maintenance wasn't the issue, then I'm just out a bit of time/miles before regular maintenance. Also, I like to add fuel injector cleaner into the tank when I do this.

lowend1

All of the above, plus a coil and PCV on the tune up. No check engine light ever.

Tom Jackowski Jr.

I had a similar issue with loss of power in my 92, where it felt like it was about to stall but then would recover. A new O2 sensor fixed it for me. The previous owner put a Bosch O2 sensor in there, and from what I've read, XJs are particular to NTK O2 sensors, so that's what I replaced it with.