What happens when you let the clutch back out? Does the car accelerate on its own (physically sticking). THat's what happened to me when I needed to replace the throttle cable because it was frayed.
Also, when you rev the car under the hood, keep in mind you're not using the cable to rev it. This would not allow you to replicate the problem. However, are you able to replicate the problem from the drivers seat (while parked)?
