the engine management light has come on

Hi, my Astra. Engine over-boost condition comes up with a diagnostic reader, what can I do? The engine management light is constantly on. The car drives fine some-days but on others it does not accelerate as fast as normal. I plugged in a diagnostic reader and 'engine over-boost condition' and 'map circuit malfunction' appeared. I reset with the reader and the light went off for a day or so but is now back again. What should be my next step? Cheers