'88 80q idle weirdness...

[1]

I have had my '88 80q for about 8 mos now and aside from a big hole in the
heater core and a dead WOT/Idle switch it has run darn near flawlesly.  It
is actually amazing to me how well it runs at 15 years/135k miles.  The only
thing that might be considered a problem is that it idles at ~1000 rpm.  Ok,
not much to worry about especially since the idle is rock steady.

Recently on hot days (90+) when I get it fully up to temp and then shut it
off for 30-45 minutes and then start it again the idle will surge.  1000rpm,
12000rpm, 1000rpm, 1200rpm at about 3/4 second per cycle.  If it sits less
than 30 minutes no problem or over an hour again no problem.  I assumed it
was the ISV so this evening as it was ideling I disconnected it expecting it
to settle down.  It didn't.

Any ideas?  There are no codes, and once things cool down some it will be
fine again.  the ISV is very warm to the touch but so is everything else
under the hood.

Oh one other thing, the 1000RPM dle will drop to 800RPM if I turn on
something that draws a lot of current like the rear window defroster or if
the cooling fan comes on.  Also when the idle is surging it will sometimes
settle down when the fan comes on or I turn on the rear window defrost.
Weirdness.

Thanks in advance for any help,

Rand Soper
Portland, OR
'88 80q