There could be many of things wrong on why a 1986 BMW 325 I will not stay running. The most common thing that happens when a car will not stay running is because the spark plugs have went bad.
dd
get a new engine DUMMY!
Its out of gas
lack of fuel
check ignition
to me it sounds like your map sensor is going out, you might want to check that.
weak fuel pump.
dirty carb bowl or water in the carb
you can but it wont stay running if the battery is dead
check for a vehicle theft system?? Is the Light Illuminated. does it stay on:::
Have you checked the alternator?
have a pontiac 6000 2.5 motor and it wont stay running