Just got my son's "new" '87, and we were told by the seller it had an idle
problem.  He's driven it about 200 miles with nothing more than a bit of an
idle surge once in a while, but now it won't idle at all cold, and when it
warms up for a couple of minutes it races up to 3000 rpm and stays there.
Restarting doesn't help, and only when I unplug the idle control valve will
it stop (die).

I've checked the TPS with an ohm meter and it works fine, and the idle valve
hums.  I can't find any vacuum leaks (propane torch probe), and it was
recently tuned up.  So, is it possible for a bad Idle control unit to cause
this?  It seems odd that an engine can run at 3000 with the throttle closed!

The only way to test it is to replace it for $200.

Thanks!

Stuart