Date: Tue, 4 Sep 2007 02:39:57 -0400
Reply-To: "T.M." <tinkerman007@YAHOO.COM>
Sender: Vanagon Mailing List <vanagon@gerry.vanagon.com>
From: "T.M." <tinkerman007@YAHOO.COM>
Subject: Re: It's time to hit that idle Stabilizer on the head!!!
On Mon, 3 Sep 2007 22:33:14 -0700, John Bange <jbange@GMAIL.COM> wrote:
>From his comments, I understand that the
>> original boxes were analog, and jumped through considerable hoops to
>> derive the signals needed to operate. The replacement digital unit that
>> would use the IC's would have no such problems, and not be so
>> problematic.
AFAIK, the main thing that usualy breaks in those boxes is the output
driver transistor, due to overheating caused by the ICV solenoid sticking
(pretty much like a stuck electric motor), causing current overload and
destruction of the transistor, sometimes also the current limiting
resistor. The analog circuits seem to work fine.
>Exactly. The old analog device manages to keep the engine at a certain
>number of revolutions per minute, despite the inability to ACTUALLY COUNT
>either revolutions or minutes.
No need to "count" - as I mentioned, it's full of analog op-amps, which
are probably used as integrators ("counting" pulses) and oscilators (to
generate the pusles to drive the ICV). Plain & simple good-old analog
circuitry...:-)
> Doing it digitally is a simple matter of a
>program that loops through the following instructions:
>
>1. measure time between coil "sparks" to get idle speed
>2. is idle too low? open ISV wider
>3. is idle too high? close ISV a bit.
>4. go to 1.
>
>The throttle switch throws it into a "standby" condition,
More importantly, it also puts the ECU in "standby" condition so it
doesn't interfere with the ICSU (some signals go in parallel to both).
> and the PS pump switch merely modifies what it considers optimum RPM.
Yep, so does the A/C sensor switch.
> Easy as a walk in the park, really.
Once it's working of course...
> I'm actually surprised they didn't just include this function
> in the Digifant. It would have been so easy.
They should have. It's probably Bosch's trick to make more money (and VW
too, also for replacement parts. Can you believe the ICSU costs more than
the ECU?).
>The project stalled on the one thing I couldn't figure out: how, exactly,
>does the idle control unit operate the idle stabilizer valve? Having but a
>voltmeter, I can only tell that it receives voltage when the ignition is
on.
>Without some insight into how it's opening and closing the thing, I'm
>stumped.
OK, I'll try to take a look and get you this info, but since my time is
limited, help from the list would be good (that's why I wanted to put the
photo's on the web). What is needed is to reverse engineer the output
driver schematic and put a digital scope on the output.
One of the problems I can think of is the mechanical design of a
replacement device. Maybe piggy-backing on the original circuit board
inside the original box using the same connector would be the easiest
solution.
>--
>John Bange
>'90 Vanagon - "Geldsauger"
