Hi all, I have a 2002 st170 (Bluefin, K&N, Peco cat back). I have a problem with the way the car drives - at around 3k revs the car starts to 'shudder' while accelerating.....it gradually increases speed but doesn't ever 'clear' itself. This is only a recent thing. I have checked the plug gaps (1.30mm) and it has been put on a diagnostic and no faults came up....help me please.......