Date:         Sun, 16 Aug 1998 13:07:38 -0700
Reply-To:     Austin <austins@IX.NETCOM.COM>
Sender:       Vanagon Mailing List <Vanagon@vanagon.com>
From:         Austin <austins@IX.NETCOM.COM>
Subject:      pesky throttle switch
Comments: To: vanagon@vanagon.com
Content-Type: text/plain; charset="us-ascii"

At 10:09 AM 8/16/98 -0700, you wrote:
>I've been having an ongoing problem with my throttle switch. The symptom is
>that _sometimes_ the engine doesn't idle properly. The idle hunts up and
>down between about 1000 and 1600 rpm. The problem occurs mostly when the
>engine is cold started. Once it reaches operating temperature, the problem
>goes away. I have traced the problem to a throttle switch that sometimes
>doesn't close at idle.
          >snip<
>It's as if the throttle valve is sticking and preventing the switch from
>closing. Yesterday I called a dealer to inquire about obtaining a new
>throttle body. $680!! Not an option.
>
>Another odd thing I observed is that the switch behaves differently when the
>engine is running. <SNIP-KEY CLUE FOLLOWS:> It always closes properly at
the >idle position when the engine is off. The switch will only fail to
close at idle >when the engine is running. It's almost as if the air
rushing through the throttle body keeps the throttle valve from closing all
the way sometimes. If I'm >driving, a sharp tap on the accelerator will
usually cause the switch to close >properly.
>
>Mark McCulley
>87 syncro Westfalia
>
As our VG's start aging, this may be a problem that crops up more often.
Had a pair of Solex 40mm sidedrafts (on an NSU - ex SCCA CSR that I raced
on dirt!!!) that were old, & the butterflies wouldn't return to idle unless
you blipped the throttle (or the engine was off).  The problem was that
engine vacuum at idle creates a force of ~ 13 psi, or ~25 lbs of pressure
which is carried by the butterfly shaft bearings (bushings, actually); as
tiny as the bushings are, they're quite heavily loaded.  Eventually the
bushings wear into an ovoid/egg shape, allowing leakage & sticking.
(sometimes the shafts wear out - or both!!...fun!).   So anyhow the
solution (pricey) was a set of Webers, since they used ball bearins &
seals, all readily replaceable.

My solution for the Solexes, which I'll apply to the throttle body when the
time comes, was to remove the butterflies/shafts, & either replace the
bushings if they're there, or in the probable worse situation wherein the
shaft is running directly on the throttle body parent material,  I'll have
to bore the throttle body & install: 1) preferably, sealed needle bearings,
or; 2) bushings machined from Vespel SP21 (teflon infused polyimide-NOT
nylon).

Austin