Long self. If cng is installed then first check emulator and advancer. Otherwise stopping after start refers to weak current or Low fuel so in addition to tuning, check following:
Spark plugs
Ignition coils
Plug wires
Battery condition
Fuel pump
How is fuel air mixture ratio? Check tail end of your silencer...if dirty or blackish or oil sluggish then Lean air fuel ratio will be issue
Long self also occurs if self is not serviced since long. So get it serviced with petrol too