1998 Saturn SL2 Idle jumping and Car stalling

Engine Mechanical problem
1998 Saturn SL2 4 cyl Automatic 110000 miles

I have a '98 Saturn with high mileage (around 110, 00). My car will start cold and run but once it warms up the idle jumps way up and down (can see the RPM pin bouncing). This happens in park too. When it stablizes it continues to idle high. Then, when I come to a stop (especially if its a sudden stop) the car will stall. While sitting at stop lights the car will rev and try to stall randomly. Putting it in park and giving it gas will usually keep it running. When it does stall it doesn't want to start up again. I have to floor the gas pedal and then rev it for a minute before putting it in drive or it will just die again. It will start up with no problem when cold. I've stopped driving it-this seems serious. I want to know if the problem is so serious I should just call it a lost cause. I don't want to just start throwing money at a car this old. Any ideas? (The engine light goes on and off, as does the check oil light even though the oil level is fine)