I have recently acquired a 1991 Volvo 940 SE. Could anybody tell me what to expect as far as symptoms of the Turbo going out.

If the turbo is in fact dying, you'll typically have a lot of blue smoke coming out of the exhaust after getting into boost. Typically occurs when you've driven the car hard and then coast for a while. When you accelerate, it'll let out a large plume of smoke. Will look like a land-based crop duster. Another sign will be a high pitched squealing when you're above 5 psi of boost. That'll be the sound of the impeller touching the housing while the turbo is producing boost. Expect decreased performance after a couple years or so of the smoking, since it can plug up the cat, which will cause your performance to suffer greatly. It will also begin to sound more like a 940 with a non-turbo engine when the cat is plugged.

-J