[T3] Problem solved, but Why?

[J. Jonik]

Re:   71 Std FI Sqbk, w/ 73 engine

After running great after previous problems solved by replacing Voltage Regulator, suddenly, on sleeting day, engine started fluttering, vibrating, etc, at one point not wanting to rev with acceleration in first gear.
 Made it home.  Next day, it started up easily (despite temps in the high 20s), but still had that fluttering syndrome.
 So, just to eliminate the easy probs, I simply made sure all wires were snug on their connections,  and all hoses too, and widened point gap just a little (it was a tad too narrow), and re-set timing, and did a gently "scrape" of points and rotor and dist cap contacts.
 Voila!   Engine (again) sounds and feels brand new.

But, which of those things did the trick?  That is, what might cause that "fluttering"...the sense that the engine was doing sort of raspberry...kind of like the effects Woody Guthrie used in his song, "Riding in my Car Car".
  https://www.youtube.com/watch?v=DUDtFdnn9oQ  
Was this an injector or spark plug connection?  A ground wire? Plugs at Dist or TVS?  One dirty contact in dist cap?
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