The one listed on craigslist in San Mateo?

You can mess with the ACC vacuum lines and switches but most likely the vacuum actuators are shot. On these cars the most sensible course of action is to remove the dash and install a fresh set of actuators. Many will agree this 20 hour job is the easy way Replacement diaphragms are available in the aftermarket but they don't work so well in dual mode pods and if you crack the brittle clips holding the pod halves together you need new pods anyway. Good time to swap in a dash with no cracks if the existing dash is cracked and such things bother you.

My money's on the front cover of the vacuum pump if it's an old style vacuum pump (no exposed bolt heads on the front cover). Maybe the gasket between the pump and the timing chain cover. If it's an old style pump, consider a later style pump as old style pump failure can take out the timing chain.

I think you know the answer to this one Seriously, my rule of thumb for normal/not normal is this - would you pay $50K for a new car that behaved that way?

This is not a common topic for 87s. Start with the basics - is there a strong exhaust smell outside that the AC is sucking into the cabin? Does it look like there's an exhaust leak anywhere along the exhaust manifold, turbo and downpipe? Maybe the flex section of the downpipe?

Sixto
87 300D