I've got a v70 2.4 petrol (2002/51 reg), has been running perfect until now, started it earlier and sounded like it was miss firing, and would Rev up to 2500 rpm then drop back tick over and keep going forward and back to 850-2500 with no input from me, and no power, message on dash- engine Service needed urgent, and the emissions fault light is on ( transmission shaped light) HELP PLEASE