I have a 1.9 cdti Vivaro and more often than not the engine fault light is on.If, as sometimes happens, it is not lit, then i get a fault like an air flow restriction and engine seems to surge. If the light is on, then it runs fairly normally. It will only rev to about 3500 rpm. I have changed the air flow meter but this has had no appreciable effect except to increase revving by about 100rpm