Date:         Sun, 3 Dec 2000 18:54:51 -0500
Reply-To:     James Creech <jacreech@VISUALLINK.COM>
Sender:       Vanagon Mailing List <vanagon@gerry.vanagon.com>
From:         James Creech <jacreech@VISUALLINK.COM>
Subject:      AFM resistor surface & idle valve opening
Content-Type: text/plain; charset="iso-8859-1"

Greetings to All!
I'm still hunting down the cause of my poor cold idle - but getting closer
thanks to your help.  A couple of questions I haven't seen asked / answered
yet, if anyone knows the answers:

(1) AFM
The Bosch FI book speaks of the AFM (if I'm getting it right) increasing air
flow volume logarithmically (vs. linearly) in relation to vane (flap)
travel.  But how about the resistance track?  Is it logarithmic also? - I
would think not, rather linear.  i.e., Is there a linear increase in
resistance as the rotary contact moves across it?  Knowing that would help
evaluate how the metered resistance should increase as the flap moves:  If
it is a linear relationship then the ohm values should rise in a linear
fashion from the very start to the very end of the flap's travel.  I can put
an ohmmeter probe in various places across the track - or of course just
read the resistance in the normal test spot at the AFM terminals as per
Bentley, but if mine is defective that might not help me.  I would like to
know what it is SUPPOSED to do by design.

(2) Idle Speed Stabilizer Valve
I understand basically what it does (allows air to bypass the closed
throttle to compensate for the unique needs of idle).  But what goes on
inside?  I want to know so I can do a few more tests on mine to see if it's
good or bad.  Does it (a) pulse open and closed rapidly?  (b) open when
needed to a manufactured (predetermined) opening size and stay there til it
closes completely - i.e., either open fully or closed fully, nothing in
between?  or (c) open to varying degrees depending on need (the various
engine conditions "read" by the ECU via sensors, throttle switch, etc.)?
Bentley says in one test the correct current to the valve should be a fairly
constant 430 mA, but in another it will vary from 430 mA to a full 1 amp.
That might mean (if it is an electromagnetic valve) that is opens to
differing degrees depending on current supplied by the system.  I want to
know this, hoping I can actually watch my valve open and close and know if
it is doing so properly.

Thanks!  (and sorry for the verbiage)
Jim Creech
87 Westy GL, 2.1