I have a 86 vanagon with 128,000 miles.  Just replaced the engine with a
new rebuilt from Boston Engine.  Here's the problem:  When I first start
it up after sitting overnight, everything is normal.  Idles at 800-1000
rpm but "bucks" a bit until it has run for a minute or two.  After it has
warmed up to normal operating temperature, it will idle at about 2000
whenever I'm stopped at a red light.  Then when I take off from the
light, it will hesitate and start very slowly as if it is starving for
fuel until I get it up to about 2500 rpms.  After that it runs and sounds
normal.  I have replaced the O2 sensor, re-checked the timing (its
correct), and have replaced the distributor cap.  I also tested the idle
speed control and it seems okay---vibrates like the Haynes manual says it
should.  So, what do I check next?  Any suggestions from the list?
Thanks in advance.

Larry in Lincoln