The idle when the A/C is on is adjusted by the idle stabilizer control unit.
If you have a friend with a '86 or newer van, try swapping in his known good
ISCU.  That way you can easily tell if it is the culprit.  I have new ones
available but they ain't cheap so it is best to be sure this is the problem
before swapping in new ones.

Thanks,
Ken Wilford
http://www.vanagain.com
John 3:16

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