Hello group, new guy here.

This is what I've got and my problem.

I've got a 1987 YJ with 90,000 miles on a 4.2 with a 5 speed
Problem is it sputters and the rpms drop randomly at idol, also when I
hit the clutch or when the RPM's drop quickly it drops down almost to
stall and then kicks up to 750-850 rpms with a miss fire or sputtering
sound.

other that that it runs great, good pick up, starts up first time, every
time and does not diesel on me at all and never has.

It started doing this back in early June and since it started I have
given it a complete tune up, Cleaned the carburetor, got a brand new
distributor on e-bay really cheap and replaced that, and a new coil. I
have re-timed it and re-tuned the carb a couple of times. also the carb
was rebuilt 50,000 miles ago from it sitting for so long and not running
(Previous owner).

at this point my best guess is that the carb needs to be rebuilt again
or the timing chain needs to be replaced.

Does anyone have any ideas

It would be greatly appreciated

Thanks