1994 Chevy Corsica car loses power

i have a 94 chevy corsica v4 157,000 miles and when i start up my car it drives normal for a while than it loses MOST of its power i notice when this happens if put the gas peddle to the floor it revs all the way up an gives me back the power but than i lose the power agin after a few mins. and the car shuts off sometimes when its got no power! but allways starts back up. and when the car has no power the motor sounds funny.