1993 Pontiac Grand Am Car loses power and dies at idle

This car was my grandfathers and he took great care of it. The problem is when the car is in idle. If you are in park or neutral, the car will idle up and down. Down to the point it dies at times. It surges after warm up, not when cold. If the car is in drive or reverse with a "load" on the engine, it doesn't do it while you have the brake pushed and are stopped. What gives? Also the dim lights work but when you flick the lever back for brights, all the lights go out. Even the dim. The brights do work if you just flash them, but not when on permanently. They go out and so do the dims. Any answers are appreciated. I just acquired this car, so I have no idea of all of the past maintenance.