1993 Buick Regal Rough idle, stalls, hissing sound

This isn't a common parts store part like spark plugs and water pumps. You will likely have to visit the dealer or a salvage yard. The stalling is due to "unmetered" air getting into the engine. When it doesn't go through the Mass Air Flow sensor, the Engine Computer doesn't know that air is there so it doesn't command enough fuel to go with it.

If you do ask at the parts stores, just pop the hood in their parking lot and point. They're used to that. The guys at the dealership will be able to tell you if new parts are required or if new clamps are all that's needed to perform a repair of the existing parts.

Caradiodoc

Can't say for sure without seeing it, but it sounds like a part of the PCV system. That will bring blowby gases into the intake system to be burned. If the other end attaches to the fresh air tube coming from the MAF sensor, it is supplying air to the crankcase and the air will be cold. More likely it's bringing the blowby from the crankcase to the air intake at the throttle body since that's where you said it is attached. A rubber tube would work but oil vapors tend to cause it to deteriorate very rapidly. Being metal suggests oil vapors, hence, part of the PCV system.

The tube can't be part of the EGR system because the hot exhaust gases aren't introduced at the throtle body, and that sad plastic clamp would melt.

If this pipe slides onto fittings at each end, you might find replacement hose in bulk at the parts stores. If there are special ends, bolt-on flanges in particular, it is more likely to be a GM-only part. Still doesn't hurt to ask at the parts stores.

Caradiodoc

You're most welcome. I hope it helps. If you get the chance, post a note telling where you found the parts and what it took to make the repair. That could help someone doing a search in the future.

Caradiodoc