When you mentioned the brake booster not functioning as it should it triggered a recent memory of a part I've replaced (a week ago). https://www.fcpeuro.com/products/volvo-booster-vacuum-ejector-s60-v70-xc70-s80-xc90-genuine-volvo-30665561 Car ran like utter crap, (braking was horrible too) if the h...

Having had many encounters with failed ignition coils, I'm going to say that is your last concern. Were it an ignition coil you'd feel it most prominently under acceleration, not lifting off the go-pedal. Also, symptoms of a failed coil are constant, not intermittent. You will eventually run into a ...