Automatic or manual? The brake booster and brake assist vacuum pump and their connections can cause vacuum leaks. Poke around and see if any of the little red plastic locking bushings are broken. You can also pull the brake booster line out of the top of the intake manifold and plug it to see if the idle smooths out. Just don't let whatever you plug it with get sucked into the intake, or you're gonna have a bad time.
(Former) Saab Tech / Competition Prep