Or any parts attached. Basically my understanding is the accumulator has vacuum reserve to run the turbo when heavy throttle eliminating vacuum source.

Some cars have a vacuum pump to increase vacuum when using enough throttle to reduce vacuum. I don't know if X5 is one of those

A vaccum leak anywhere can cause your symptoms. Find the leak. Let us know what you find

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2011 E70 • N55 (me)
2012 E70 • N63 (wife)