'95 90qs: Cut Out, Hard Starts, Stall

[Dan Z. Johnson]

Hello,
My 1995 Audi 90q (73k miles) has a real problem. It started
as the occasional stall at idle, then progressed to quick,
intermittent cut out while driving. Now, at road speeds, the
engine will sputter rapidly and die altogether, and be
nearly impossible to restart. Car backfires slightly. After
letting it cool a bit, I can restart and sometimes run for
1/2 hour or more with no problems.
At first, I thought that i had gotten a bad tank of gas. Ran
some methanol through, with limited, short-term success. may
not have helped at all, in retrospect. I am two tanks of gas
past that first suspect tank. I have run injector cleaner
through before and after this started. All panel indicators
are normal.
Any ideas?

-DanZ