lack of power

Hi, can anyone help? have a 99 model v70 t5 which runs with a very slight misfire (well i think it does) - it also lacks the serious pulling power and just lately keeps cutting out. have just had it serviced by volvo dealer who says its running ok but needs new "spark plug leads" ( i told thrm that if they can find them they can fit them). the engine mang light came on 2 days ago - have had it checked today by tuning specialist who plugged into car a got a error code P1618 - which apparently does not exist - he thought engine ecu may be faulty - don't know what to do or where to go - any suggestions????