Sounds very similar to the problem I just figured out with my '80 Westy 
(2.0L FI).  I experienced this whole thing while 600 miles from home, fun :(  

 I was having problems with it missing when at high revs ( 40 mph in 2 or 65 
mph in D, yes it is an Automatic).  In addition it was dying when I would 
start up from a red light.  When I checked the spark plugs they were black 
and sooty yet no smoke out the exhaust pipe.  The points looked good and so 
did the cap.  I also checked the timing.  When I adjusted the fuel/air mix 
screw nothing changed (quite odd).  It got progessively worse.

I checked the air flow meter like Bentley says.  It passed all the tests.  
So next i pulled the wire off the "Cold start valve".  BINGO.    Apparently 
my thermo time switch is bad and it is being "choked" all the time.  Still 
have to test a couple of other things in there with the volt ohm meter but i 
think i found it.

>From reading the Bosch book on FI make sure to test your cold start valve 
and your cylinder head temperature sensor that feeds into the FI system 
computer.  The temp sensor is the most important sensor in the system ($44 
at the VW dealer).  Mine was suppose to have about 2-2.5K ohms at 68' F.  
When I tested it showed 8K ohms at 100' F (i live in AZ).  It is suppose to 
have less resistance as it gets warmer.

Matt