Saab Engine Cutting Out???!?

Hello. Lately my 1991 Saab 900 with 201,000 miles has been giving me some trouble. While I'm driving, sometimes the engine RPM's bog down to under 1000 and the engine and car shake and knock, and then then engine will cut out. Hitting the gas only makes the engine bog more and shake more. Also sometimes when i come to say a stop sign or light, the RPM's will also go down, so i have to hold my foot on the gas. What could this be? The Check Engine Light comes on randomly as well, but never when any of this is happening. Remember this is only sometimes, the rest of the time it runs fine. What could this be!?

it actually sounds like your turbo (most saabs are turbocharged right?) and if you have an old engine/turbo with over 200,000 the bearings or something of that nature could be causing the turbo not to spin. since the exhaust powers or goes through the turbo before out the tailpipe it could be suffocating your engine. also the air that goes into your engine is sucked through the turbo so if it isn't spinning no exhaust is getting out and air is not going in.