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another high idle problem 87 5kcst auto tran

Hi list,

After a stretch of highway driving at around 85, I noticed as I was slowing
down coming into the city that the idle was unusually high, as if the cruise
control were stuck on.  Flipped the cruise switch, no improvement.
Disconnected the cruise module, no improvement.  Put her in neutral, the tach
rises quickly and steadily to 3000.  Work the throttle, the rpm goes up from
3000; release throttle, rpm slowly comes back down to 3000.  

Later at home, I check the ISV.  There's no crud and it seems to be operating
freely (hoses off, electrical on, you can see the valve oscillating).
Reinstall the ISV, unplug the green connector on firewall, idle rpm still
climbs to 3k.  Unplug the electrical connector to the ISV, same high idle.
Unplug the WOT switch, same high idle.  Undo the ic/tb hose and check the
plate in the throttle body--it opens and closes fully and freely.  Throttle
linkage is fine.  Unplug the ISV temp sensor, no change.  Unplug the ECU temp
sensor, no change.  Ground each temp sensor connector, no change.  Swap the
temp sensor connectors, no change.

Could the idle speed adjustment screw cause this problem with a broken o-ring?

Fuel distributor air flow metering plate stuck?  Spring broken?  

The car is automatic transmission.  Anyone remember what that trick was 60
Minutes used to induce unintended acceleration?