1998 Mazda 121 Metro is randomly stalling

The first thing to do is drive the car yourself and see if there’s a pattern to what’s happening. Until then, you have even less idea of what’s going on and a diagnosis is all but impossible at that point. You might find that the car is cutting out after a period of driving (maybe caused by a dirty fuel filter) or when the engine reaches a certain temperature (possibly a sick crank angle sensor).

I’d also recommend an electronic scan to see if any fault codes show up. These codes can be very specific and will often lead you straight to the root of the problem.