Date:         Sun, 16 Aug 1998 10:09:29 -0700
Reply-To:     Mark McCulley <raven@HALCYON.COM>
Sender:       Vanagon Mailing List <Vanagon@vanagon.com>
From:         Mark McCulley <raven@HALCYON.COM>
Subject:      pesky throttle switch
Comments: To: vanagon@vanagon.com
Content-Type: text/plain; charset="us-ascii"

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.

I replaced the throttle switch with a new one (new cam too) and adjusted it
to the specs in the Bentley manual. No fix. When the switch fails to close,
I can pull back on the lever on the throttle body and the switch will close.
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. So I proceded to completely disassemble
the throttle body and thoroughly clean and lubricate the moving parts. I
adjusted the throttle switch to specs and reinstalled the throttle body.
Again, no fix.

Another odd thing I observed is that the switch behaves differently when the
engine is running. 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. This doesn't seem
possible to me as the return springs on the throttle valve are quite strong.
To put this in perspective, the specs for adjusting the switch are in the
range of 0.05 to 0.1 mm. So we're talking fractions of a millimeter here.
(The measurement is made with a feeler gauge between the throttle stop screw
and the throttle body). Again, when the switch fails to close at idle, I can
make it close by pulling back on the throttle lever on the throttle body. If
I'm driving, a sharp tap on the accelerator will usually cause the switch to
close properly.

The only solution I can think of is to increase the switch setting above the
spec'd 0.1 mm until it works properly all of the time. I did this once
before but I opened it up so much that it affected my gas mileage. I guess
I'll try this again, changing the setting incrementally until it works.

If anyone has any experience adjusting the throttle switch and can shed some
light on this problem , I'd appreciate it.

Mark McCulley
87 syncro Westfalia