Arrrrrrrrgh! Intermittent dead 90q ignition (long)

[nde264 at lulu.it.northwestern.edu]

I've been having intermittent ignition problems with my 89 90q with 214000
miles for over a month now.

The symptoms/problem are as follows.  While driving the car, or more correctly,
while running the car it will sometimes just lose ignition, as if someone had
just turned off the key.  The tach drops to zero.  Sometimes, while driving,
with the engine still turning, the car will just buck and spring back to life.
This is accompanied by the tach needle bouncing.  When I do lose the car
entirely, it will usually restart after 5 or so minutes of sitting.  The car
will run very well, like nothing ever happened, for about 10 minutes and die
again.  I believe that I have isolated this to the ignition system as the fuel
pump does run immediately, autocheck flashes OK, etc. when turning the key off
and back to the run position before trying to restart.  I just get NO spark.

In the past month, I have replaced the distributor/hall sensor and ignition
control computer with units sourced from Chris Semple.  Neither of these fixed
the problem.  I looked through the schematic in the bentley with an electrician
friend, and he told me to get what is referred to as the ignition booster in
the bentley.  I bought a NEW ignition coil/module from pap-parts, and the car
drove fine from Dayton to Chicago and drove fine for most of this week as well.

I thought that this was a thermal issue as it usually happened after the car
had been running for a while.  Well, yesterday, it happened while pulling out
of a parking lot in which the car had sat for 3 hours.  It was still light
outside, so I swapped out the new ignition coil/module for the old one, still
no start.  I returned to the newer coil and then swapped for the old ignition
computer, still no start.  I try both old computer and coil, no start.  At this
point, I can smell gas coming from my exhaust.

I pull a spark plug and set it on the valve cover, no spark when turning the
engine.  I pull the coil->distributor wire, set it on the strut tower brace, no
spark.  I then run the tests listed on pages 28-130-1 through 28-170-2 in the
Bentley manual.  Everything tests fine.  The diode test on the hall sensor
(28-160-1, first test) provided what looked to be a constantly on LED, but
maybe the pulses were too quick for me to resolve (starter turning engine circa
300 rpm, 5 revolutions/second, therefore either 12.5 or 25 pulses/second)?  Is
my hall sensor fried and consistently closed circuit when hot (as it is
effectively a transistor)?

After an hour and twenty minutes of tinkering and testing, I am thoroughly
disgusted and decide to wrap it up and call a friend for a ride home.  I slam
the hood, try one more time, and as unburnt fuel fumes pour from the exhaust,
it miraculously starts.  Drives beautifully for 10 minutes and stalls again.
It's dark out now, and I sit in the car for 5 minutes, starts, drives home.

I did not drive my car to work today, as I am afraid of it.

Am I missing something?  Where else should I look?  Is it possible that the
keyed ignition switch is failing, though it still performs all other functions
it should?

I'm debating wrapping up this 90q and getting another vehicle if I can't
diagnose/fix this easily/cheaply.  I love my car, and would hate to see it go,
but the rage is setting in.

TIA,

Nathan Engelbert
89 90q