Hi, I'm new to TDi engines. I have a 2003 seat Alhambra 1.9 TDi with a terrible misfire when you put your foot down/under load. I've had the codes read (nothing showing up), I've changed the fuel filter, air filter, MAF sensor and injector wiring loom. But none of that has helped. Idles nice and runs lovely with a light foot. What could this be? Many thanks