1997 Opel Astra Stalling

Engine Performance problem
1997 Opel Astra 4 cyl Front Wheel Drive Manual 45000k miles

I have recently had my Opel Astra stall or quit while I am driving. Sometimes it won't restart for quite awhile. Other times, it seems to run like a champ. I recenlty added plugs and had the timing reset. The problem still occurs.

It seems that when the car is full of gas, it doesn't seem to happen as often, though there may be no connection.

Any assisitance is greatly appreciated.