loss of power due to exhaust fault on vauxhall zafri?

I drive a Vauxhall Zafria SRI 1900 (120bhp) While driving one day the engine management light came on and reduced the engine revs to 3000, l took the car to my nearest vauxhall dealer, they floored the throttle and pluged a laptop into the car and told me to take the car for a long hard run once a week, Today the car is again sitting in the dealers garage with the same problem only this time the car would not drive anywhere, this time they have told me that a filter needs to be replaced and that l need to drive the car on a long journey in low gear and high revs so this problem does not happen. Does anyone know what is going on, is it only vauxhall, do l really need to drive a car in this day in age like this.