I have some problems getting my automatic transmission van to
consistently idle when stopped at a light, especially if the idle is
set at 900rpm.  I need to set it higher.

I have a voltmeter attached to my oxygen sensor and it is indicating a
very lean mixture.  I have the air-fuel screw on the AFM almost all
the way in (clockwise).  When I get home tonight I'm going to try and
move the ratchet wheel inside the AFM that controls spring tension.
Then, adjust the air-fuel mixture screw again.

I'm new to these diagnostics.  For a while, I assumed that my van was
running rich because there is black soot on the tip of the exhaust
pipe.  Does black soot on the exhaust indicate a rich or lean engine?
Or, is it possible that the soot could be an indication of either
condition?  It seems to me that I can smell unburnt gas from the
exhaust.  However, this could just be my imagination?

The O2 sensor reading indicates the engine is lean.  The soot makes me wonder.

Before I fiddle with the AFM, I thought I would ask the friendly vanagon people.

Other info:
  - O2 sensor is less than 6 months old
  - new fuel filter, air filter, fuel pump
  - new spark plugs, plug wires, rotor, distributor cap

Also, I have a vacuum guage from Sears that I never used.  I may tap
it into my vacuum hose system tonight for a test.  Where Should I
connect it?  I can't detect any vacuum leaks with ear or carb cleaner.