Its a gasser, vacuum is everything. If there is a leak, sure it can hurt performance. The vacuum systems run right off of the intake manifold. If there is a leak then it usually has a really bad idle or wont get any power at higher RPM. From what you describe it sounds like a few problems.

And FYI, the locks have their own pump in the trunk to operate the vacuum lock pods. Vacuum is not used for ignition cut-off, ignition switch kills spark instead. But it does tie to the brake booster, HVAC, Evap system (fuel tank fume recovery) and a bunch of other little things like EGR valve.

Im tired, so I am forgetting things probably but I hope it helps a little.

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1991 560 SEL / 185k miles
1992 750il / 17k miles - project car