Say, did you ever find cause or fix to your 93 Cabriolet "sudden loss of power" issue?

My 92 cabby just started exhibiting the same "sudden loss of power" issue. Road grade doesn't seem to matter, though originally I thought issue manifested only when going uphill.

The car starts solid, and runs fast & fine when driving; but there's a periodic, yet regular, loss of engine power for an interval of 30-40s, after which the engine/power suddenly kicks back in and car again drives fine?!

When in neutral and with foot on pedal, the engine will initially hit a RPM, then fall back down to idle; then ~20-50s later jump back up to the original RPM ... with no change in pedal input.

Appreciate any advise or info you may have gleaned re: your problem; thanks!