Idle Problem

["vrvader" <vrvader@xxxx>]

I have a question based on my idle. (I have an 81, 5 speed)

When I start the car it idles as normal (after an initial high idle 
and then kick down in a few seconds). As I drive and stop the car 
seems to idle fine.

After about 20 minutes of driving when I come to a stop the car 
wants to idle at 1500 - 2000. If I blip the throttle it does not 
seem to make a difference. If I rev the engine up close to red line 
and let it fall down it tends to drop to around 1000 RPM ( a little 
high still but better).

I have opened the engine bay during one of these high idle sessions 
and pushed on the throttle and it did not make a difference so I do 
not believe it is based on a sticky cable or such things.

What may be causing this?

Thanks in advance for your advice