Date:         Mon, 13 Aug 2001 15:19:48 -0400
Reply-To:     Ed Carroll <ecarroll@MAINE.RR.COM>
Sender:       Vanagon Mailing List <vanagon@gerry.vanagon.com>
From:         Ed Carroll <ecarroll@MAINE.RR.COM>
Subject:      throttle position switch
Content-Type: text/plain; charset="us-ascii" ; format="flowed"

The throttle position switch adjustment and eccentric cam blues

Executive version: Is the eccentric cam adjustment component of the
Digifant throttle position switch a function of the switch body, or
of the throttle valve body?


Background: I was trying Saturday to track down the fault in the
Digifant system for our '87 which has caused varying degrees of
intermittent rough/surging idle, highway bucking and most recently
some episodes of hard starting and low power, especially climbing and
often accompanied by moderate blackish smoke.

After testing several components, I checked the throttle position
switch and found that it wasn't opening -- infinite resistance --
until a centimeter or so into the throttle, and wasn't closing again
until the very very end of the valve's movement.

Further investigation showed that the tightening screw was pushed all
the way to the left extreme of the slot it rides in, that is, the
switch was positioned furthest away from the idle stop.
Unfortunately, the adjusting screw (which operates the eccentric cam
mechanism) is barely recognizable as a screw. It looks like it was
the same type of high-shouldered allen-head screw as the tightening
screw, but with the hex interior rounded out and one half the head
blasted as if by punch and hammer.

I found that by loosening the tightening screw almost all the way, I
could reach under and slide the switch body in the right direction
and clamp the switch down again. But I could only get it scooched
over far enough that the switch opens about 1 millimeter from the
idle stop; spec.s call for .05 mm to .1 mm. I could tell also that
the switch is no longer in the right plane -- I apparently dropped it
away from the adjuster to manually slide the switch in the right
direction.

Question: If I drill out or otherwise permanently remove the damaged
screw, as appears necessary, where does that leave me? Do I have to
remove the throttle valve from the intake at this point to repair and
regain full function of the adjuster? Is the adjuster built into the
throttle valve body, or is the adjustment function somehow built into
the switch?

Thanks for any help.

Ed Carroll
'87 Weekender
'69 Karmann Ghia convertible