RE: re Vacuum leak - HELP (resend)

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

The ISV hoses are the first on the inspection list.  I'll let you know what
I find.

Also, has anyone tried grounding the manifold ground wires elsewhere - like
the firewall?  That stud is mounted through aluminum with a steel bolt,
resting on a brass washer from some other component - talk about a crappy
grounding surface!  It's a virtual corrosion magnet!

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


-----Original Message-----
From: Smith, Kirby A [mailto:kirby.a.smith@lmco.com]
Sent: Tuesday, February 16, 1999 9:18 AM
To: 'sinclair@prospro.com'
Subject: re Vacuum leak - HELP (resend)


You wrote:


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.
-----------------------------------------
A leak that faked me out for a while was in the hose from the ISV to the
mainfold; it had split on the bottom next to the 90 degree bend.  Also check
your grounds at the intake manifold.  It is possible for the wire lugs to be
tight to the stud, but the stud loose in the manifold.

                .... Kirby   (Kirby A. Smith)
                              2 x 1988 90q
                          New Hampshire USA