> I've a couple of sharp electronics buds here, and with them, I want to
> pursue development of a digital replacement for that little box that
> causes so much trouble. Actually, I will probably be more like a
> sidewalk superintendent than a pioneering engineer. My buds will pursue
> this with my direction and encouragement.
>

I took one apart and made a partial rough schematic with the intention of
doing the same thing. Thing is, it's a really tense array of op-amps,
capacitors, and resistors-- a wacky analog computer doing a job better done
digitally. My conclusion is that emulating that crazy thing at the component
level is doing it the hard way. The best way to approach it is to treat it
like a "black box": monitor its outputs while twiddling its inputs to see
what it does. Heck, you can even figure most of that out from reading the
Bentley. Really, a 25 cent PIC microcontroller could easily do what those
hand-tuned analog crazy boxes do, and do it much simpler. Controlling the
idle is a simple matter of watching the RPMs and opening the ICV when RPM is
too low, and closing it when it's too high. The advantage digital
microcontrollers have is that they can 1) count, and 2) tell time. That
analog circuit trying to measure RPM without either of those capabilities is
a masterpiece of "old skool" engineering, but totally yesterday's news.
Abandon ye the old way and start from scratch. All it does besides monitor
RPM is watch a couple switches on the AC and power steering to push the idle
RPM up a notch when needed. I've been meaning to build such a thing for
months, but I've had a "minor" complete engine-transmission-hoses
replacement to take care of. Another 500 miles and the engine will be broken
in and I might be able to start work on that again.

Anyway, I have a couple broken ones I got from Frank Condelli for $10
postage. I'll send you the one I didn't disassemble for $5 postage, if you
like..

--
John Bange
'90 Vanagon
"We'd tell a monkey how to peel a banana, if he said he was peeling one in a
Vanagon."