Date:         Thu, 18 Feb 1999 08:41:33 -0500
Reply-To:     matt greenwell <mgreenwe@CECASUN.UTC.EDU>
Sender:       Vanagon Mailing List <vanagon@gerry.vanagon.com>
From:         matt greenwell <mgreenwe@CECASUN.UTC.EDU>
Organization: University of Tennessee at Chattanooga
Subject:      update:another gremlin (throttle position switch)
Content-Type: text/plain; charset=us-ascii; x-mac-type="54455854";
              x-mac-creator="4D4F5353"

just a quick synopsis of a recent fix, in case there are some of you out
there silently suffering from the same problem.

original post:

----------------------------------------------------------

wondering if i'm crazy...

this is going to sound a little weird, so bear with me. i have an 87gl
westy. recently, i cleaned the motor and transmission exteriors with
gunk engine brite and a power spray (local spray and wash). this is
something i have done a number of times, with no ill effect
(electrically, and etc.). well, after the last wash, i noticed that the
van is....well...hypersensitive to that moment between acceleration and
deceleration at around 3000 rpm. that is to say, cruising down the road,

at around 3000 rpm, if i take my foot off the gas, there is a noticable
jerk as the van goes from forward torque to reverse torque. when i give
it gas again (same rpm) there is another noticable jerk as the van goes
from reverse to forward torque. at low speeds (1st gear) when this
occurs, the jerk takes on whiplash like proportions. the van didn't used

to do this. the jerk is not accompanied by any clunking, or differential

noise, and the van otherwise runs perfectly (a relative term). the van
shifts smoothly, and i can move through the gears from 1st to 4th with
no problems...the problem surfaces only when i'm "coasting", alternately

pushing and releasing the gas pedal to maintain speed, and again, its
worse around 3000rpm. i realize that a certain amount of this "jerking"
thing that i'm trying to describe is perfectly natural, and i have begun

to wonder if it's all in my head, but after driving it around town
tonight, i'm convinced that the van is driving differently than normal.
that  the "natural" jerk has been somehow amplified.

i'm wondering if, as a result of the power spray, i've lost some sort of

electrical connection, fouled some solonoid, or some other such thing
that would explain this behavior. before you ask, i did check the
electrical connections on the distributor, and checked the inside of cap

for moisture. no moisture, and, while the wiring harness (which is
attached to the distributor) is showing some wear, everything seems
intact (and my guess is the van wouldn't run at all if this wasn't the
case). my gut instincts tell me that this is somehow an electrical
problem (distributor, sensor faulty wiring, etc), not a mechanical
one-but i'm open to any suggestions. this is one of those things that i
can learn to "drive around" but ...well, its difficult to describe how
profoundly irritating these little gremlins can be. if anybody can help,

it's someone here on the list.

matt greenwell
87gl westy
chattanooga, tn

---------------------------------------------

thanks to both karl bloss and mark mcculley for sending me, in essence,
the following information:

> Matt,
>
> You may have affected the idle/full throttle switch on the throttle
> assembly.  Look at the throttle assembly and find the throttle cable
> coming from the front.  With the engine off, move the throttle as if
you
> were just tapping the throttle pedal.  You should hear a tiny click.
This
> switch tells the ECU that the throttle is at idle and this triggers a
> number of effects.
>
> The effect that you should now be interested in is that the throttle
> switch cuts off fuel injection if you're coasting with the foot off
the
> pedal.  BTW, Darrell Boehler's Digifant tool shows you this.
>
> If you want to get more into it, do this:  On the '87, it's a single
> switch that does both idle and full throttle.  If you take off the air

> cleaner and throttle assembly, you should see the place where the
switch
> is.  Again, check for the click.  You should also see the cam and
switch
> assembly.  Check Bentley for the exact removal procedure.  I never
really
> removed mine...the switch wasn't bad, but the cam was bent from years
of
> use.  I used some needle nosed pliers to get it back to functioning.
> Bentley has an elaborate method for checking spacing, but I didn't
bother
> with that.
>
> FWIW, my symptom was the FI wasn't cut off (i.e. the switch didn't
close
> with my foot off the throttle) and the van would backfire when
> decelerating.
>
> Hope this helps.
>
> -Karl


----------------------

a quick investigation revealed that the throttle position switch had
literally
fallen off of bottom of the throttle body (it looked like it was just
glued into
place with some epoxy). so, 10 minutes to take off the throttle body, a
little
bit of pc-7, and i'm back in business. in a later e-mail, karl informed
me that the digifant's, in particular, are prone to this problem because
of the way they are mounted. i wonder now if this thing had been
disfunctional when i bought my van, if i would have ever noticed the
problem, so heres hoping that this info will do somebody some good, and
make your van a little easier to drive.

matt greenwell
chattanooga, tn
87gl westy