something similar to this happened to me while I was test driving a 92 VR-4. After I put in the clutch, the RPM's wouldn't fall. After shutting the car down and pushing it to the side, I saw a box on the drivers side of the engine bay, I believe it's for cruise control, where the cable was getting caught up in. After pumping the gas a couple times with the car off, the slack in the throttle cable was eventually drawn up, and it worked without a problem. I think it may be solved with a little oil on the throttle cable.
This sound like your problem?, anyways, that's my experience