Hi, whilst driving recently on the motorway, I found that when I pressed the accelerator pedal down hard, the engine was very hesitant. It struggled to pick up. The engine seemed to be jerky and unresponsive. It only did it when I pushed the accelerator down fully and I had to release the accelerator pedal to keep going. If I accelerated slowly and smoothly, it didn't happen. I have tried it since and it still seems to be doing it. It felt like a fuel problem to me, but I have no idea really. The car is a 57 plate Ford Focus TDCI 1.8 manual. Can anyone offer some advice?