Check out what's on the SID (Saab Information Display,) when you start the car. It will run a self-diagnostic test and let you know whether there are any problems on the engine, brakes, airbags, car alarm etc etc. Also try to find out when the turbo was replaced - as the chances are that a 900 will have done over 100,000 miles.
I don;t know where you are, but try finding an independent Saab garage and see what their advice is.
