I just drove the car to lunch and before leaving on the way back I removed the oil filler cap while the car was running. It came off with about the same amount of force as it does when the car is not running, and once it was open there was a whooshing sound. I believe one of the symptoms of a failed/failing AOS if excessive vacuum that makes it very difficult to remove the oil cap.
Just adding a little info to the thread.
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