I have two 2006 transits, that both suffer from this (both started it at about the 50k mark)..
One tho, has the added symptom of idle revs increasing until you kill the engine, which resets it.
We where also told that the EMS diagnostics wont log the fault unless it has been left idling with the fault for some time.. the amount of time was never specified, and since killing the engine and restarting it clears the fault, it's unlikley that anyone would sit for 20 mins going nowhere.
As both are still under warranty they where passed back to the dealer, who, as the above poster says, ordered new throttle pedal units..
Be warned tho.. we were told that, due to parts manufactures shutting down, they are becoming harder to get hold of.
Doc, December 2008