Date:         Tue, 30 Sep 2003 20:51:02 -0700
Reply-To:     Philip Chidlaw <pchidlaw@MCN.ORG>
Sender:       Vanagon Mailing List <vanagon@gerry.vanagon.com>
From:         Philip Chidlaw <pchidlaw@MCN.ORG>
Subject:      Re: The "Other" Vanagon Syndrome, Part II
In-Reply-To:  <20031001012428.37758.qmail@web14508.mail.yahoo.com>
Content-Type: text/plain; charset="us-ascii"

Likewise, desert-like terrains. Roughly mid-Nevada Hwy 50 after the
longest, straightest, flat run of that long trip with an AFM with < 5000
mi. Textbook case. I have always assumed a harmonic vibration resonance
not unlike the VW Tech Bulletin 92-01. I have since added the capacitor
fix but not repeated that same Hwy 50 test. Yet. My family insists on
recharged ac before any more desert trips. Coastal weaklings.

Philip Chidlaw
Gualala, CA

-----Original Message-----
From: Vanagon Mailing List [mailto:vanagon@GERRY.VANAGON.COM] On Behalf
Of Harald Rust
Sent: Tuesday, September 30, 2003 6:24 PM
To: vanagon@GERRY.VANAGON.COM
Subject: Re: The "Other" Vanagon Syndrome, Part II


The afm-caused intermittent syndrome has been an
enigma. Volkswagen designed the harness as a
fix, and dealers have installed it on good afms.
The afm harness is not supposed to fix a worn out
air flow meter. It is supposed to stop the
intermittent bucking/stalling syndrome.
That syndrome has nothing to do with a worn out afm,
but a worn out afm could cause it as well.
There has been much speculation as to the cause
of afm-induced intermittent syndrome.
I wouldn't be surprised if even Volkswagen doesn't
exactly know the cause of the erratic behavior of
some afms.
Some speculate that it's the air flow meter flap
oscillating as the air flows through.
If the flap starts vibrating, it could send an
erractic signal to the ecu, which would make the
ecu shut down until it's reset by turning off
and restarting.
Another cause could be static electricity building up,
maybe due to the air flow through the afm.
Static could send erractic signals to the ecu, causing
the bucking.
I have only noticed the intermittent syndrome in
desert like terrains.
That made me think of static buildup around the afm.
The cap seemed to fix that.
Another cause probably could be a worn afm resistor
board, but that should be easier to detect and replace
the afm. You can also easily test the afm with a
multimeter, as according to Bentley.
Harald
'90 westy
James wrote:
Thanks for the explanations.  The decriptions as a potentiometer makes
it clearer to me.  What I still don't understand is, why the problem
only manifests after sustained cruising.  Why doesn't the van always
stumble when the AFM crosses the "bad contact" point? I cruise control
to work for 20 minutes and have never had the problem.  Yet, after a few
hours of similar cruising on the road trip, it happened.  Not that any
of this theory matters, really - just curious. James 90 Carat


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