vauxhall zafira 03 diesel how to turn off engine management light?

car has had light on for 8 months, has passed mot in that time with no emission problem but despite rac and vauxhall dealership trying to find fault (P1032) no success. Vauxhall had car on diagnostic and mechanic spent 2 hours and still could not diagnose problem. Car a real pain as engine limiter keeps coming on though car never fails to start first time and never stalls etc. Anyone know how to just get rid of the light and stop limiter coming into effect?