TLDR: I have a similar problem, but no answers, sorry…
Wow! What you’ve described is almost identical to what I have experience with my 97 wrangler (2.5 I4 150 MT US). I’m going to include the description (and evolution) of my issue here, in hopes that someone can help both of us.
The Initial Problem:
Engine has short misfire at 1750rpm under medium acceleration (whether in drive or stationary); under hard acceleration misfire becomes near-stall. At 3000rpm, no noticeable misfiring, but engine would ‘tremble’ under load: the acceleration would decrease and become inconsistent. At high loads (uphill) some intermittent misfiring and power loss occurs. The only other noticeable symptom is a long crank time to start. Usually, if the engine is cranked for at least 3 seconds, then stopped, then cranked a second time it will start up ‘right away’ on the second go. Depressing gas peddle to any depth has no noticeable effect. Priming fuel lines has no noticeable effect.
Things I’ve Tried:
- checked for vacuum leaks
- verified spark with inline tester on each cylinder
- swapped out upstream, downstream, and then both 02 sensors: no effect
- swapped out throttle position sensor: increased idle speed on startup, but otherwise no effect
- swapped out crankshaft position sensor: misfire has transitioned to weak backfire at 1750 rpm, otherwise no effect
I was going to check the timing with a gun, but as you pointed out the Distributor appears nonadjustable. One other thing of note: I currently have a bad EVAP solenoid, and have until now considered that an unrelated issue. Does your vehicle have a bad EVAP as well? Mine almost never throws a DTC but I’ve confirmed with a multimeter that it is quite dead. I have not checked the timing chain on my engine yet.
Finally, the local mechanic I used took a look at the car before the CKP was replaced. His testing found that the computer was indicating Lost Crank Reference (which when stored should be p1374) but the CKP was consistently putting out signal. Additionally, the lost reference was not occuring often enough to result in a stored DTC.
Patrick