Date:         Tue, 6 Oct 2009 14:38:15 -0400
Reply-To:     David Beierl <dbeierl@ATTGLOBAL.NET>
Sender:       Vanagon Mailing List <vanagon@gerry.vanagon.com>
From:         David Beierl <dbeierl@ATTGLOBAL.NET>
Subject:      Re: Stupid Question...... Gasket between AFM and airbox. 1.9 wbx
Comments: To: T Collins <tonycollin@gmail.com>
In-Reply-To:  <aeea9b480910061100r3c336c1dhc1d87f3e0ee1a416@mail.gmail.co m>
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At 02:00 PM 10/6/2009, T Collins wrote:
>That makes sense. I was trying to see if that was the reason fro erratic idle.

Please describe as well as you can idle and circumstances.  RPM
range, how often, how long, cold/warm/both etc.  Cheap handheld tach
from FLAPS if necessary.

>  If I take the [potentiometer] cover off while the engine is idling
> I see the arm of the [potentiometer] in the AFM shake and to the
> tune of the erratic idle.

The wiper arm of the pot will always oscillate at idle, which gives
you an idea of how fast the AFM system can respond.  It also
preferentially wears the track in that spot.  And of course it will
shift up and down as the rpm changes.

>Then again it maybe that darn TB or its TPS.

TPS is easy to check; measure voltage across the switch (either one
if you have the two-switch deal).  If the switch is properly closed
you'll see zero volts, if open probably five.  What else are you
concerned about with the throttle body?

What is the timing doing when the idle shifts?  Normally it should be
jumping all around within a several-degree range.  I don't know at
what rpm the idle stab disengages -- it's entirely self-contained,
all it sees is the signal from the distributor, so it knows nothing
about throttle position etc.  I'm guessing 1000 rpm or less.  I used
to know, back when I had an '84.  You can find out by seeing at what
rpm the timing smooths out.

Is the stabilizer (box with two plugs on left firewall forward of the
coil) connected?

What changes if you shut down, unplug it and connect the plugs together?

Have you checked for vacuum leak where the cooling pipe that crosses
the top is attached to the intake pipes (one or two locations, I
forget)?  It's relatively easy to tear a mounting stud loose, which
will give a variable vacuum leak that can be a stinker to find
because it looks totally normal until you try to lift it.

Yrs,
D