why does the engine control light comes on when driving?

i have a cavalier 1.6 petrol on a J plate (jan 92) and the engine control light comes on occasionally when driving, more often lately. it doesnt matter what speed i am going or if its a short or long journey but the engine appears to stutter, the light comes on briefly then the engine picks up again. i have checked all the possibilities and everything appears to be normal. any ideas?