1990 trans am-jerky idle

my buddy is borrowing his little brother's trans am and is thinking of keeping it to fix her up. the car cruises like a 5.7L but seems to hate idling at the stop lights. he puts her in neutral to keep the jerkiness to a minimum. any pointers on what this might be?

is it a dead miss or what? could need a new distributor cap, or rotor button, plugs, wires.