Greetings all!

My mechanic tells me that the computer in my '86 Vanagon is for some
reason failing to properly control the idle speed, with the result
that the idle-speed-adjustment-screw needs to be turned way down to
keep it at around 1000 RPM.  Also, replacement computers are
apparently about $800.

Having some knowledge of embedded computers, but no specific knowledge
about auto computers, it occurs to me that it might be possible for me
to build a replacement, at a parts cost considerably less than $800.
However, I don't yet know enough about the program the thing is
running, or the complete list of tasks that it performs.

Can anyone point me to more information?

Many thanks!

-jeremy bornstein