(S) 1.3 multijet turbo lag

Hi have a punto grande 1.3 90 diesel this car was terrible accelerator just did not work either on or off .But hey something has happened and its now superb i can accelerate from low revs and the power delivery is excellent no lag honest what have i done dont know I have started using millers diesel sport 4 with total excellium diesel fuel and thats all i can put it down to i was ready for selling this car but i kid you not the difference is amazing