Date:         Tue, 30 Sep 2003 18:24:28 -0700
Reply-To:     Harald Rust <harald_nancy_vw@YAHOO.COM>
Sender:       Vanagon Mailing List <vanagon@gerry.vanagon.com>
From:         Harald Rust <harald_nancy_vw@YAHOO.COM>
Subject:      Re: The "Other" Vanagon Syndrome, Part II
Content-Type: text/plain; charset=us-ascii

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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