hi guys i have a problem with my st170 , just recently it has started hesitating whilst accelerating at 4000 rpm+, i have recently serviced it and have replaced plugs and leads , still no different but this is only happening when the engine is warm .

i have also tried a different coil pack and the same is happening does anyone know what the remedy may be i dont think its a fuel problem as i have change the filters and have also cleaned the tank out and the car allways runs on optimax !!! so any suggestions would be gratefully appreciated thanks guys !!!