Car brought in by RAC hard to start wont rev up clean and engine smokes badly. Scanned system and only 1 code sensor 1 oxygen sensor fault. we have replaced that. Seems like plugs are fouling up.temperature sensor readings are OK. There seems to be a lot of crankcase pressure when oil filler cap is removed. Car fills workshop with what seems to be oil smoke.possibly a blocked breather?any advice would be grateful.