1996 Chevy Lumina Acceleration

I have a 1996 Chevrolet Lumina and recently it has not been accelerating well whenever I stop at lights. It is on and off, sometimes it will accelerate well from start up, other times it will idle at stops and despite how much I press down on gas pedal, it will refuse to accelerate. I checked the spark plugs, and there is one that seems to have rusted on top near the wires. It happens so randomly I question whether to drive that day. Please help. Thank you.