2000 Explorer revs when clutch pedal depressed

[MattBG20t]

My parents have a 2000 Ford Explorer 5-speed manual and when the clutch pedal is depressed the revs climb to about 3000rpm. After a second or two the revs will drop to a high idle (about 1750). My guess is that it has something to do with the fact that the car has been driven only a few times a month in the past year since my father has been in Iraq. Any suggestions as to what might cause this problem? I'm thinking something is stuck open or closed...