If you ever wanted to know what is inside the VW factory AFM harness I've
posted some pictures on my web site.
As everyone knows, this harness was sold by Volkswagen to address what we
refer to as "Vanagon Syndrome".
VW part number is 025 906 302.
It is an active device consisting of an op-amp and some resistors.  The
"Capacitor Fix" seems to work for some people, although it is passive in
operation.
See
http://www.telusplanet.net/public/gary2a/rack/afmharness/afmharness.htm

Gary Lee
http://www.telusplanet.net/public/gary2a/rack/vanagonrack.htm