I have a 170,000 mile S line Avant Tdi 140 bhp which until recently has been running well, it has had the belts changed when needed, as well as the oil pump drive replaced. Last service was an Audi long life and it has had a recent service which was just oil and filter. It has had a re map at Performance Tourque about a year ago whihc improved this no end. Recently I have noticed a bit of a misfire/hicup when accelerating on the motor-way, or along roads when under load, say overtaking, when cruising on light throttle loads the car runs fine. Starting has been a bit hesitaint, but I put this down to the recent cold weather. I am fairly mechanically minded as I build old race cars, but donl't want to tinker with my everyday run about, plus most of it is electronic. I plan to change the fuel filter this week , but if this does not cure the misfire under load what should I be looking out for next?