Problem with running the discover

Hey guys whats up? Ive never been here before in the forum. Anyway, I have a problem with one of my dad's cars. He has a 1998 Landrover Discovery LE. Well, the car sometimes does not start....when im at a light the car just turns off and stalls. When i am driving on the highway, the car will turn off but then turn back on because i keep my put on the gas. I checked the battery and the alternator and its not the problem. Does anyone have any idea what the problem is? Thanks a lot in advance!

Try new plugs, wires, distribtor, and rotor if that hasnt been done lately.

or maybe a fuel filter..

did you get a check engine light while this was happening?you should have.it could be a variety of reasons for this to happen both mechanical (fuel supply)and electrical(engine control).also don't forget to check your engine module fuses(this always stays forgotten).