Bob,
You're not the only one who has this problem.  My 1984 has a nearly
identical problem.  When rock cold, the van runs perfectly - it pulls away
cleanly.  Then when it gets a little warmer, there is a zone where if you
pull out below ~2000 rpm (I'm guessing - no tach), the van sputters and
nearly stops dead, which isn't pretty when you're trying to cut into
traffic.  Once the van gets up to full temp, it seems to get better.

I haven't begun troubleshooting, and I figured the list may have talked
about this many times over.  However, since the post has been raised, I
thought I'd chime in as well.  My van has a mysterious white wire coming out
of the airbox - is this the "VW recommended little wiring harness at the
AFM?"  The previous owner told me that he put in a new AFM prior to my
purchase.  I also notice that my van runs WAY rich - the exhaust stinks to
high heaven, smelling just like my dad's old 1966 MGB.

Thanks for any suggestions the list has for Bob and me.

Chris