I also have a 2004 saab that I have been letting my son drive to college. He came home over the weekend and it has a problem idiling. I put some gas treatment in it. but it's still doing it any suggestions. Thank you SillySally

Try some general maintenance things first. Check air filter and replace if necessary, clean throttle with throttle body cleaner, clean or replace Idle Air Control valve or Mass Air Flow sensor depending on which one your vehicle has also change fuel filter if have not done so in awhile add Lucas Fuel Injector cleaner to gas tank.

$5.00 breather hose check valve on top -center of engine compartment