Date:         12 Dec 1995 09:54:04 -0800
Sender:       Vanagon Mailing List <vanagon@vanagon.com>
From:         "Harvey Chao" <Harvey_Chao@smtp.svl.trw.com>
Subject:      Re: '87 goofy idle

                      RE>>'87 goofy idle                           12/12/95

>.  I took the 
>idle stablilizer valve out and cleaned it. Checked it out by putting 12 
>volts across it. It would just rattle back and forth making me guess 
>it still had some life. How do you know if its ok, should it hold the 
>piston at one end or is this hammering typical.  Anyhow, I checked 
>the voltage to the valve and got a reading of 10.7 V.  Yet, the valve 
>does not hum - hummmm.  Suggestions appreciated :)


>I then took out the FI black box behind the rear right tail light. 
>Cracking it open revealed a lot of potential questions.  There were a 
>lot of components that had black spots.  One black component that 
>looked like a voltage regulator (thin approx. 1/16 thick x .3 x .4) 
>with 3 prongs was blackened on the circuit board as well as itself 
>:(.  Bunch of the 3.3 uF capacitors are leaking yellow stuff, etc... 
=======================================

There a couple of things that come to mind here.  

1) By applying 12 volts and feeling the piston snap closed, and by shaking it
and feelilng the piston(?) rattle back and forth, you have made a gross
verification that the valve will probably operate properly if fed the correct
input signal.  As others of the group have mentioned, when working properly
you should be able to feel the valve "hum" as it rapidly opens and closes in
response to the applied voltage.  Under normal conditions, 12 volts is applied
and then turned off very rapidly.  This allows the valve to pass variable
amount of air depending upon the ratio of valve open to closed time.  I don't
know if this is achieved by varying how long the "on" voltage is applied
(pulse width modulated), or if the valve is cycled faster or slower (frequency
modulation) - either one can achieve the desired result.  However - if you
attempt to measure the voltage applied to the valve's electrical terminals
with an analog or digital meter, you will get some reading less than 12 volts
due to the AVERAGE applied voltage over time being less.

2)  Your description of the FI black box would indicate some potential failed
components.  I have heard of a number of cases where the power/output
transistor "One black component that looked like a voltage regulator (thin
approx. 1/16 thick x .3 x .4) 
with 3 prongs was blackened on the circuit board" may have overheated/failed
due to lack of adequate heat sinking, trying to provide power to too low a
resistance due to shorted wires or shorted winding in the idle stablilzer
valve, or even due to overheating because somehow the frequency  at which it
was driven got too high causing internal device heating.

Without proper documentation or readable standard parts markings, this is a
tough one to repair, unless you can find or borrow an identical unit that has
readable parts markings.  Also, this module may well have CMOS chips in it
that are very sensitive to Electro Static Discharge damage, you should set up
an appropriate ESD workstation before you attempt repair.

The capacitors, 3.3 uF,  are probablyh stock items you should be able to get
pretty readily.  I would imagine that a D.C.  working voltage of 18-25 volts
should do nicely, higher would be better if you have the space.   the fact
that they are leaking indicates age, poor quality, high temps.  If they look
like a minature cylinder with an aluminum shell covered by plastic insulation,
they are probably std. aluminum electrolytics.  It is also possible that they
could be tantilum electrolytics (smaller  and more expensive than aluminum,
but generally higher quality parts).

Before you break down and throw money at a dealer, you might try a used unit
from a wrecking yard.  I believe that this is a BOSCH made unit, simiilar (but
probably different) from the ones used in BMWs, and what I hear from that
on-line net group is that these boxes are fairly ava#005#ilable and cheap at
wreckers  => that they are pretty reliable.  Most reputable yards will
guarantee a "good" module.

Harvey