I just had this issue happen today and have started looking into it. At first I thought the throttle body might be sticking but then when it started to rev further than I had depressed the throttle to begin with I knew it had to be more than that. The weird thing about it is that when the car slows to a stop, below 5mph, the engine will return to normal idle rpm. Above 5mph though anytime the clutch is in or I am out of gear the engine revs to around 5,000. Obviously I would like to be able to look at the engine while driving but having my hood open and going +5mph might be a safety hazard... The other thing I was thinking is that my cruise control could be acting up as this is the only other thing that can act on the throttle body to rev the engine, however i made sure that it was switched off while I was having this issue.
I will keep looking into it and if I figure out anything, I'll be sure to pass it on. If anyone has some suggestions I would like to get this fixed as well without taking it to a shop and paying for it.