Chris:
I am trying to T/S the same problem. Here is how I am going about it. The
 way I see it the cause could be in two areas:
1>Mechanical i.e. Air bypass valve, throttle, throttle cable, etc.
sticking allowing too much air in. This would simulate slight pressure
on the gas pedal holding the idle at 2000 rpm.
2> Electrical i.e. The ECU forcing the Air bypass valve to stay open or
advancing the timing. 
Since the ABV (air bypass valve aka control valve for idle stabilizer) is
common to both check it first. During high idle unplug it. If it is still
idling fast your valve is stuck! (23.56% probability). Some judicious use
of carb cleaner and then silicone lubricant might be in order. If normal
or no idle is obtained the ECU is forcing the valve open for some
reason.(37.62% probability). This seemed to be my problem. The next
place I went to is the coolant temp sensor for the ECU. Mine checked out
of tolerance. I substituted a resistance appropriate for the engine temp
and the idle INSTANTLY returned to normal. "Cool"; I said. I purchased a
new sensor from VW for $10.
Good Luck
Ken Lewis
kdlewis@juno.com
86 VW crewcab