Been super-backlogged on email,  but just wanted to follow up on this,
since I know I enjoy hearing the resolution to problems posted here.

As a recap, I had been experiencing poor performance (rough running)
coming off idle, and the van had been cutting out sometimes (bucking
and jolting) while cruising down the road.

I went through all the basic checks, and turned up two irregularities,
which I believe explain the two issues.

1. Although they looked OK visually, my spark plug wires measured out
of spec (too high) on resistance.  One of them was actually open
(whoops).  I recrimped that one, and swapped one other for a spare
(that still measured out of spec, but not by as much).  No more engine
cutouts.  Will be putting a new set on order shortly.

2. When I tried to adjust the idle mixture (aiming for just rich of
stoich using the O2 sensor), I found I couldn't get the mixture to go
lean, even with the AFM adjustment screw totally removed.  This would
seem to explain the poor performance coming off idle.  I could get the
mixture lean only by adding a big air leak after the AFM.  I also was
able to get the mixture lean by fudging the signal from the AFM to
ECU.  I suspected maybe an excess fuel pressure issue, but the
pressure and regulator operation with manifold vacuum were spot on,
which leads me back to the AFM.  Not Vanagon syndrome, but out of
calibration.  AFM out of warranty, vendor said I could send it back to
the refurb guys for calibration.  Rather than be without my daily
driver, and also based on positive list comments about new Chinese
parts vs. re-re-rebuilt originals, I put one of these on order:

https://www.aliexpress.com/item/32972721257.html

I'll let you know how it works out.

For now, I have the AFM mixture adjustment screw all the way backed
out (had been at the "stock" position as supplied, 4.5 turns out
IIRC), and this helped substantially with driveability off idle,
though there is still a little bit of roughness/hesitation.

Happy motoring,

Alex