I am not sure if this will help but sometimes changing one thingis like a daisy chain. My car was running fine but I replaced the plugs for the hell of it. The next day I tried 98 RON fuel as well. Then it started to misfire at idle in drive. So I was screwed as to what caused it. After much jerking about (making sure # 5 lead ddint touch #6) I replaced the plug leads. Now sweet as a nut.... and now I know it want the fuel change.
rev@IRC. EB 3.9 auto. VDO head unit, Focal and Sony speakers, tinted, mags, pacemakers, hi-flow cat, 2.5 inch exhaust, K&N, slotted.