The make, model and engine info would help.
check for a vehicle theft system?? Is the Light Illuminated. does it stay on:::
bad alternator, dead battery.
dd
A Ford 1999 Expedition engine is probably not seized if it will start and idle but will then not stay running. This could be due to a clogged fuel system, faulty injectors, faulty spark plugs or a wiring problem, or even a faulty distributor.
Sounds like no gas is getting to the carb. Fuel pump maybe.
Its out of gas
get a new engine DUMMY!
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.
you can but it wont stay running if the battery is dead