93 Escort - Engine revving when clutch is depressed / in neutral

Can anyone give me a starting point to diagnose my baby? I've recently taken on the responsibility of doing all of the repair work myself. I've had a couple of successes, but they were small jobs. Now I fear something
more complex is afoot and I don't want to start tearing it apart until I know where to begin.
I have 93 Escort LX - 5 speed - 1.9L with a slight problem. After traveling 70MPH for more than a few minutes, I exit the interstate and come to a stop light / sign. With the clutch all the way to the floor and / or the stick in neutral, and no foot on the gas, my engine revs back up to 2-3K rpm. I can put it in gear again and continue driving at lower speeds, but with the revs kicking back up whenever I push the clutch in. If I turn the car off for a while (go into a store), the problem goes away.
Thanks to anyone with some help! Anthony
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says...

My first guess would be throttle position sensor going bad.
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