Vagag

My Fabia 1.2 TSi estate 60p.s. model has developed a slight hesitation under acceleration or misfire between 1200 and 2000 revs when in 4th or 5th gear. It could be an engine management issue e.g. the anti pinking management, a fueling problem, a spark problem or an electrical connection. As it was due a service, my independent mechanic replaced my plugs and fuel filter with my choice of NKG iridium and bosch filter despite these not being due as I'd already replaced them at an earlier service immediately after buying the car second hand. The engine still hesitates under load. Has anyone else experienced the problem? Where would the smart money be investigating first? I have the heat shielded high tension cables to my plugs by the way and have seen the posts on that subject, but am not discounting the possibility of these needing replacement. I should also add that I have managed to activate the anti detonation control when in low revs under acceleration (when I first owned the car and was seeing how flexible this engine is) and I'm pretty sure that's not the problem. No engine management or other warning lights and I am very hot on keeping up the service schedule with top quality components.