basd fuel
If it starts but doesn't stay running after you release the key from the start position, it means your ignition switch is bad. Not a huge expense.
The make, model and engine info would help.
It could be your EGR valve.
to me it sounds like your map sensor is going out, you might want to check that.
That would be a tripod. Tripods have 3 legs and are made to stay in one place.
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.
If your alternator is good it should stay running until your engine dies from no fuel.
animals can stay safe by running/fighting or hiding.
You stay in shape
It out of gas...
dd