Random stuttering, is my distributor broken... again?

[Beatnik]

I have 2.0l OHC (from Sierra) in my MK1 Escort and it has started to randomly stutter and backfire when driving at low rpms and while doing the engine braking etc. When it starts doing it, it also barely idles and usually dies when I stop. It starts happening randomly and the problem exists a varying period of time at once (10min-30min) and about 50% of the time I drive, The other 50% of the time absolutely no issues. It doesn't matter whether the engine or the outside temperature is cold or warm, it can start and stop happening almost anytime. The problem is always as bad or completely non existent, nothing in between.

Usually it goes like this; I'm about to go to work, it starts fine, drives fine and I have no issues during the whole 30min trip, BUT when I'm about to leave back home after work; it starts, but doesn't want to idle, I have to give gas to keep it running and usually have to restart couple of times until it stays running. The whole trip back home it stutters at low speeds, dies at traffic lights and backfires while driving downhill. Drives pretty fine during higher rpms = normal driving speeds, but I kinda hear and sense minor stutter and misfiring then too. Yesterday when coming back home; huge backfires all the way, but for the last 5 minutes of the trip, no issues at all...

Carburetor is Weber 32/36 DGV and I know those symptoms would indicate some sort of idle jet or mixture issue, but the problem is random and plugs are colored just fine and wouldn't a carb problem = mechanical problem be more consistent? Could something inside the carb get randomly stuck and unstuck? Acceleration is always normal, even when the "misfiring" is happening at low rpm/short gas pedal travel.

About a year ago, the previous (two year old) Powerspark distributor stopped working (without a warning) completely and I bought a new Accuspark distributor. Since I have issues again, I thought if something keeps braking my distributors? I run full battery voltage into the distributor as the instructions suggest. Alternator charges a bit low 12-13V. I changed plugs and plug wires, no effect.
Coil is new-ish, but I have not tried another one yet. Could coil start randomly misfiring for a period of time, but still constantly keep giving persistent sparks for the acceleration?
Engine is stock otherwise. Battery is in the trunk and everything necessary seems to be getting "ground".

I'm running out of ideas, couldn't find anything similar from Google, that would explain the randomness of the issue.

[IanSouthLincs]

I have had something similar a couple of years ago, turns out the ‘keyway’ on the inside of the rotor arm had chipped and most of the time held inside the notch on the top of the distributor but occasionally would jump causing similar issues to the ones you describe. accuspark rotor arms are very cheap so might be worth checking?

[Beatnik]

I think that was it! Thank you so much. I tried a different distributor cap with no difference and I would've never thought the rotor arm could brake from there, I though it can only wear from it's tip, otherwise being "unbreakable" piece.
I haven't had issues since I got that new rotor arm.

[Graham]

I think that was it! Thank you so much. I tried a different distributor cap with no difference and I would've never thought the rotor arm could brake from there, I though it can only wear from it's tip, otherwise being "unbreakable" piece.
I haven't had issues since I got that new rotor arm.

the other thing rotor arms tend to do is short out the spark into the dizzy shaft

[Miniliteman]

Did you have the correct rotor/cap?

[IanSouthLincs]

I think that was it! Thank you so much. I tried a different distributor cap with no difference and I would've never thought the rotor arm could brake from there, I though it can only wear from it's tip, otherwise being "unbreakable" piece.
I haven't had issues since I got that new rotor arm.

No problem at all, pleased it sorted the problem for you :-)