K11 engine jitter under constant load

I bought a 1994 K11 1.3 Micra to use as an engine donor (custom build); it supposedly has around 100k miles on it. The car stutters under constant driving at 50mph in 5th.

The engine seems to run well, but revving without load, with one of the leads disconnected (the 2nd one, always the same cylinder!) there appears no difference. The compression of this cylinder is fine. The engine revvs up well, I wouldn't say it very much short of power when accelerating. But the stuttering under mild load is quite annoying. It's less when I gear down.

I have previously replaced the injectors which elevated most of my troubles. In fact not one but TWO of the old ones had an impedance which was way of base. Including the second cylinder. The injectors I used were originally from a 75hp Nissan Almera 1.4, black colored plastic rather than white.

Replacing the ignition with a used unit did not to the full extent (other than fix the noise that was coming in over the radio!). I have new leads but I currently used those that came with the used unit.

Could it be that the second cylinder still has way too much grime and waste inside of it? Or is the cylinder bore definitely damaged? The second cylinder remains very suspect so to say but I don't know what to do next.
 
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