Factory Power Brake Fun (not really)

A rough idle indicates it might be a vacuum leak in the booster. Pull the vacuum source hose off the intake and plug the intake nipple. The idle should be good now. If so, you have a leak in the booster system somewhere. Probably the booster itself as those were trouble prone on the early A's. I'd also check the extra vacuum hoses that go to the vacuum reservoir and the reservoir itself too.