It's a switch on the pedal. Closes as you first move the pedal (similar to a brake light switch). The PCM has to see a sequence of open, then closed, before it will fuel the engine above idle. So even if the rheostat were saying "full throttle", when you take your foot off the pedal, the idle switch opens and the PCM says "sorry, I'm going to idle".

The "open-to-closed" sequence is another failsafe. It's in case you start the engine and for some reason the pedal is stuck down (think final scene of "The Blues Brothers"), the engine won't run to redline.

 

Hence...dead pedal.

 

Cool thanks.

 

Yup, common symptom of the switch not closing early enough.