i had the exact same problem a few years ago and it turned out to be bad wiring to my battery GND terminals (or 12V) cant remember. Either way it confused me a lot until i actually traced it all from the battery to its relative places and found some crap wiring. Upon repairing, the beast was perfect again.

edit: with my problem, obviously, the entire 12v rail would be gone. everything would cut out, incl the engine.. lights, dash lights everything..

edit: yeh everything would cut out ; everything! if your motor is still idling then goes back to normal rev's (when you hit the throttle) then like other members said its likely a fuel delivery problem. goodluck!