Vacuum leak - HELP (resend)

["Dan Sinclair" <sinclair@prospro.com>]

My 1988 Audi 90 has a persistent odd idle issue.  When I decelerate to a
stop, every 4th or 6th stop my idle will plunge to 400 RPM or so and surge
back up to 1000 RPM.  Fault codes reported:  Airflow Potentiometer and WOT
switch.  Both checked out in further diagnostics.  I adjusted the
Potentiometer and actually improved the situation (it used to plunge to 0
RPM rather than 400RPM!) but I suspect I've just accommodated the problem
rather than fix it.

I've been told this is a vacuum leak issue, but I don't know where to go
with that information.  I've had the injector O-rings replaced by the
dealer, the valve cover gasket replaced, and have
opened/cleaned/de-scummed/tightened and retightened the airbox, throttle
body, and intake plenum connections.  I've swapped out my ISV with 2 other
units from normally functioning cars and had the problem persist without
change.

Do I just start ordering vacuum hoses at random and installing them or
what???   I really have no idea how else to proceed besides visual
inspection which is extremely difficult given that half the hoses are hidden
from view.  If I'm going to disassemble the intake/throttle body to get to
these hoses, I might as well just replace them all no?  Any suggestions
would be appreciated.  I'm at a loss and KNOW this is not the way my car
SHOULD behave.

Dan Sinclair
1988 Audi 90, 67K mi.
Picture and details online at:
http://131.107.68.28/a4.org/registry/details.asp?car=761