Once more into the void - 5ktq high 'idle' - update

[Ben Swann]

Joshua,

 

This is simply not good information.  I'm not dinging you for trying to help -
BTDT also.  This has been a common misconception and I have a box of still
good ISVs because of it - yeah, I've owned and worked on a lot of these cars
and every one of them develops this problem at some time or another.

 

The "pinch" test you propose is not valid in most cases.  Yes, an ISV that is
malfunctioning will do this, as it has a perforated diaphragm, or may simply
be gummed up and need cleaning.  However, there are many things, most commonly
electrical that make the ISV act like it is bad.  Also, some ISVs are dual
polarity (three pins) - open normally partially and + voltage make it open and
- voltage makes it close.  Case in point is the 4KQ one is dual polarity.  The
5kq is normally closed - ISV when removed should pass little or no air - that
is the test that would confirm if it is bad or not, as they age, they may
begin to pass some air, but no need to throw it away, as this can be
compensated for.

 

The real "easy" test for starters is pulling the ISV connector.  Engine speed
should drop to "base idle" as set by the throttle bypass screw - which BTW is
another related culprit in the "idle" problems often associated with the 5kt
in particular, but not yet suspect in this case.

 

I'd hazard 70% of the time the problem is associated with bad/misadjusted
switch or broken wiring - this has been confirmed in this case.  Now he just
needs to find where the fault is.

 

Related tidbit - Idle bouncing? - That's a little different - usually a
combination of bad o-ring on throttle bypass screw and marginal bypass valve.
BTDT many times too!

 

Ben

www.gtquattro.com

 

[Date: Thu, 26 Oct 2006 19:15:47 -0500

From: Joshua van Tol <josh at spiny.com>

Subject: Re: Once more into the void - 5ktq high 'idle' - update

To: Fuzzzydog <fuzzzydog at gmail.com>, quattro quattro list quattro at audifans.com

 

Have you tried pinching off the hose while it's idling high? I think you'll
find that the idle drops when you do that, and that the solution is a new
ISV.]