My 2007 V6 Mustang left me stranded and here is a tip to get you going if it happens to you.
Was driving down the highway at 70 mph, 12 below zero, things are going fine until all of a sudden it was like someone cut the throttle cable, the engine went to idle and the position of the accelerator pedal had no effect on engine speed. Of course there is no longer a throttle cable as now we have the throttle by wire thing, all electronic. The fix was to turn off the key and restart the engine as apparently this resets the system.

 

uh... still shouldn't happen.
And that's not really a 'fix' per se

 

Did you bump your keys w/ you knee? Was the problem isolated to the accellerator or did it act like the car stalled? Did you still have your power steering? Did any lights come on the dash?

 

Sounds like your car went into the "forced limited power mode" and you're correct if you turn off the key it will reset. However when this happens there's usually something the computer doesn't like , did you check for a DTC ? I was having this for a while and mine turned out to be due to an aftermarket alarm I had installed ...

 

I thought the engine had died completely but when I coasted over to the highway shoulder I noticed that the car was idling. Of course I tried the accelerator but it had no effect. There were no codes when I plugged in the scanner. I believe the power steering was still operating as I don't recall the steering getting stiff. Was driving down a highway at 70 mph and did not accidentally hit the key. While I was coasting I did try to wiggle the key switch to see if a different position would help but it did not. I did ask the Ford Service Manager at the next town about it and he said he had never heard of such a thing but didn't have time to look at it until the next day so I continued the trip. The problem has not popped up again. I have not installed any aftermarket electrical items.

 

Did you have the yellow wrench light in the tach face on ? Sounds what mine was doing at slower speeds, but since a throttle position sensor was swapped its been fine.

 

When it happened on mine there was no DTC either , but it's always the first thing to check for. My S/C had just been installed when it started happening and so we assumed it was due to it. At first Steeda thought the S/C was causing spark blow out and that was why there was no code , but as I said it turned out to be due to an aftermarket alarm I had installed causing the computer to do weird things. Good luck , maybe it won't happen again ...