The engine completely shuts down at highway speeds when braking or accelerating moderately hard, which in turn shuts down power steering and probably the power brakes!!! this has happened four times. for each of these events, i was driving the car normally at highway speeds for an extended time, probably longer than two hours. in one incident on april 12, 2017, the engine shut down when i quickly accelerated to allow for safe traffic flow involving a tractor trailer. another incident on same day involved moderately hard braking as i approached stalled traffic on the tappan zee bridge. i was in the left lane and the road did not have a shoulder. this created a serious hazard with heavy traffic. a third incident on the same day occurred during moderately hard braking as i approached a toll booth. loss of power steering (and probably power brakes) created a serious hazard. a fourth incident occurred approximately 18 months earlier when i braked moderately hard while exiting for a rest stop. loss of power steering (and probably power brakes) created a serious hazard. in the recent three events, the "service engine soon" light turned on. the engine would not restart immediately. after less than a minute, the vehicle restarted, drove normally, and the indicator light turned off. in the event with acceleration, the engine would not restart easily for 15-30 minutes; eventually it restarted and drove normally. during the 15-30 minutes, the engine sputtered, bucked, and shut down repeatedly. i reported this issue to the bmw dealer after the first event and they said the only potential cause was water pump speed deviation. i replaced water pump in may 2016 as they recommended.