Hey Jim,
�
I suggest testing the temp II sensor.� I don't have the Bentley in front of me so I can't direct you to the right page, but it is easy.� You stick one lead of a mulitmeter to the wire coming from the temp II sensor, and connect the other lead to a ground (i.e. the base of the sensor).� Measure the resistance as the van warms up and compare to the Bentley specs.� If the sensor checks out fine, then make sure that the signal is actually making it to the ECU.� This can be done by removing the harness plug from the ECU and inserting your multimeter leads into the pins for the Temp II sensor.� I don't know which pins they are off the top of my head, but its in the Bentley.� If everything is good, you will get the same readings you got at the sensor.� If you don't, then you likely have a broken wire in the harness.� 
They may be other temperature related FI items that I am not aware of.� All of my experience is with air cooled Vanagons.� Is there a water temp sensor that sends info to the ECU?� If so, I am sure it can be tested.
Do the water cooled vans have a thermo-time switch, aux air valve, or cold start injector?� These are all temp sensitive items in air cooled vans that might produce the symptoms you describe when defective.
I agree with your conclusion that the symptoms are not consistent with a faulty ECU.� When mine went bad it would run fine until I hit a bump on the road, then it would bog down and die.� I would usually have to tap it again to get it going.� However, if there was a connection in the ECU that�finally gave out completely, it might produce the symptoms you describe.� Sure would be nice if you could swap in a known good ECU.
�
Good luck.
jake
--- On Thu, 9/11/08, Jim Felder <jim.felder@GMAIL.COM> wrote:

From: Jim Felder <jim.felder@GMAIL.COM>
Subject: Question about temp II sensor and bad running
To: vanagon@GERRY.VANAGON.COM
Date: Thursday, September 11, 2008, 12:18 PM

I'm starting a new thread on this because I am desperate to get the
van running... wife doesn't have a car without it right now.

In the earlier threads I started on this subject, I had the car
stranded at walmart. Removed the distributor for examination and when
I went back this morning, it started right up... meaning that
something in the car cooled down and the start was a coincidence or
else fiddling with the distributor connection solved the no-start
problem.

Then another problem appeared or else there was a related problem I
don't get. The car ran great for less than a minute and then started
running horribly. I barely made it home two miles away with a spot or
two of running great, but mostly horribly.

I have started it many times through the morning and afternoon. Same
thing always happens: starts great, runs strong, 30 seconds or a
minute later it's stumbling and then it stalls. I can do this until
the engine gets warm or let it cool and try it, the same thing
happens.

I removed the wires to the temp II sensor and jumpered the sensor
connections. No change. I removed the jumper. No change.

Ken Lewis has written and says it may yet be the hall effect sensor or
the ECU, but I don't understand how a bad connection or failed sensor
could create such a predictable situation of starting and then running
more and more poorly until a stall. Maybe it could, but I don't get
how.

Any ideas?

Thanks for hanging in there with me,

Jim