Hi, i have a focus 1.6 05 plate petrol, today i was driving it and it suddenly started pulling back when accelerating from a junction then seemed to be guttless and slight judder , i called rac out put on diagnostics but only came up with error of 02 sensor which he seemed to think could of been an old error? Any one suggest wha tthis could be and if is 02 sensor how much am looking at, also told possible to be coil pack? many thanks