Punto engine cuts out

Hi I'm having a problem with my 2000, 1.2, punto. It started when the car was running sluggish. I had it tested & was told it was the co2 sensor which was replaced. The problem stopped but after about 30 miles of driving the engine cut out & would not start again until the - battery connection was removed & replaced (this had to be done each time it cut out). I have been told its the ecu which was replaced with a new one but the problem continues. Can anyone please help