re. ISV?

[Swann, Benjamin R. (BSWANN)]

A defective Throttlbody(Idle/WOT) switch will cause this.  Also so will not
having any voltage to the center lead of the switch assemble, as I had found
troubleshooting about a year ago.

Ben
'87 5Kcstqw

[After a week of living with the '87 5KTQ idle at around 500 RPM, I
soaked the ISV in carb cleaner, ever hopeful that this would do the trick.
Note: without input, valve is completely closed.
Noticing the 12VDC printed on the label, but being somewhat cautious,
I hit it with a 9VDC battery to verify that it was no longer "stuck", and
reinstalled it.
Started up just fine, but on warming, the idle rose to 1500.
Unplugging the ISV drops the (warm) idle back down to 500...(Grrr)
I've been working ever since, and haven't had time to get out and mess with
it.
Its seeming :
1. less like an ISV issue, and more a control voltage issue (?)
2. like I "killed" the ISV when I whacked it with 9VDC.. (?)
3. Stop, you're both right!
In the meantime, I've left it disconnected, and just keep the idle up
"manually".
Any takers?
Thank you in advance,
best regards,
Mark Woodland]