Question for the list. I have an '82, with a TDI engine swap, that started
idling rough. Quickly progressed to the point of dying (before warming up)
a couple of times. What I found peculiar was that, when I idled at a higher
RPM (so the engine wouldn't completely die) the hesitation seeming would
repeat itself at approx 10s intervals. (And after it warmed up a while, the
interval seemed to extend to about 20s.)

I actually recorded this phenomenon in case it's helpful (or simply
interesting) in diagnosing the issue. A link to it is here:
https://soundcloud.com/user-359399352/rough-idle-consistent-repeat

Might anyone have any pointers for helping me diagnose this problem?

Thanks in advance.
ᐧ