firebird not idling correctly?

[91firebird]

I have a 91 firebird that when at a stop sign sometimes does not hold its idle and drops which then causes it to die. It starts back up fine and when moving the rpms stay up and seem to stay steady but once you stop it starts dropping low and will die if you stay stopped

 

[melsg5]

how many miles are on the car? how many miles since the last tuneup? do you ever put any fuel injector cleaner in the tank?