Have a focus cmax 07 35k miles and runs fine until a few days ago. Started to shudder and struggle a little seeming to lose power and engine management light came on. Took it to a local small garage and identified a coil issue. Bought a new one and fitted for 80 (not bad I thought). Light reset and 24hrs later back on so garage suggested could be plugs and leads so replaced and light off. Problem is it seems to ge as bad as it was with a shudder at low speed and a bug shock when I heard a bang and sounds like it came from engine. Going to take it back to garage but tonight engined popped twice. Really worried and a mate said could be an issue with the injector and not burning the petrol. Absolutely clueless and need help. Ta