Well on the surface the symptoms match a faulty Temp I sensor, The Temp
II is a good just replace because item.  I had them fail with out to
much warning, especially when a change in temperature occurs.

According to Darrell Boher's (sp) report and testing, The Temp I sensor
is a bit of a wildcard, in Pre Digifant ECU's it is more agressive in
the start up fuel map, than Digfanc ECU's, in which it's mostly ignored
until air temp is below 32 f.

Having said that, if your fuel pressure regulator is out of
specifications on the high side when cold starting, ie somewhat to much
fuel pressure, and The Temp I and Temp II are affecting the fuel map, ie
the amount of  millseconds the injectors  are turn on, for the cold
start, then you could easliy have a funky running motor, until the Temp
II starts to Come up to it's first reconizable input for reduction in
the fuel map.

    An aftermaket  Temp II, I had, when tested against the VW  Temp II
(of the same application) took about two minutes longer to reach this
first level of input.  Since then I only run VW mfg TEMP II sensors,
even though I get only 8 monthes to 24 monthes service.  Change em when
you change your coolant,.

So if this Westy has the aftermaket style Temp II, or a  Fuel Pressure
Regulator That is High, confirm by testing after a overnight cold soak,
This is one possible, but subtle, cause.

Also a maladjusted AFM spring-- a good thing to verify that it is set.
 Should yeild a .3 -.7 volts reading on the sensor lead, on a fully warm
engine that is above 3000 rpm with a load, and the O2 sensor is
disconnected.  Remember that pre cat vanagons operated this way their
whole life, just AFM spring tension and no O2 sensor

Mark