'87 Westy, 2.1l, automatic

So, thermostat's replaced and grounds and hoses supposedly checked, but
here're the symptoms I'm seeing:

Cold start:  Van acts like the battery's weak when I start it (it's
not).  Turns over quick at first, then slower, then finally jumps to
life.  Idles up and down at a low idle, sounds like plugs are misfiring,
until the engine warms up a little, about a minute or so.  Most cars
I've ever owned/worked on idle high at first to warm the engine up, or
something.  What is the cold idle speed supposed to be on a Vanagon?

Once warm:  Idles around 900-1000 RPMs, idle smooths out, puts out a lot
more stuff out the exhaust, particularly when it's cold out.  Gas
mileage has dropped from 16-17 down to 14 MPG.

Drive for 20-30 minutes into town to work:  When I'm ready to park it, I
put it in Park (yes, automatic), and the idle jumps up to 1400-1800 RPMs
for a few seconds then settles down to 1000-1200 RPMs.

I was trying to keep track of all the suggestions that have been made
here recently since the cold weather hit and everybody seemed to all of
a sudden have idle issues.  Unfortunately, there were so many different
suggestions of things to check for, I figured I better ask again.

Thanks for any and all help,
Marc Perdue