well since buying it,ive been over on fccuk,i replaced plugs (first poc),no difference,replaced 2 coilpacks as (2 were snapped and flapping about),replaced the maf and cleaned it with electrical contact cleaner,i also cleaned out the EBV and left to co pletly dry,i also cleaned the air filter..no difference. I then bought a new Lambda Sensor and inspected plugs at the same time,to which i noticed the plugs and old L/S were covered in soot which was a bad case of over fueling.
Since cleaning the plugs and fitting a New lambda,the car pulls like a train now.
If your car is backfiring then that is a sign of over fueling.
Hope thats some helpul info to you