1999 Volkswagen Golf engine problem

Engine Performance problem
1999 Volkswagen Golf 4 cyl Four Wheel Drive Automatic 108k miles

i have a golf 1999. It runs the short distances normaly. It rolls and it slowed down normally. But when I use the freeway to roll a distance of more than 10 milles, when I sttoped in an intersection for example, the engine turns off while stammering, it suffocates, the accelerator does not answering, I must accelerate severale times to becomes again normal. I suspected the quality of fuel may be contains a little of water or it is not suit for the engine. But observed that the rhythm of the engine changes when I turn on the air-conditioner and the engine shut down when I trie to move the car while stammering with an abrupt noise. I want to now what is hapenning in my car and how or where I can fixe it.I will jappreciate your assistance enormously