I have a skoda fabia 1.2 classic 

 

the car started with an idle problem, when it was idled the revs were going up and down however not all the time, most of the time it was fine.

It still has the idle problem but now has a random misfire especially when you accelerate hard and tonight driving home it seems like when it use to just misfire seems like its stuck so it has no go but then goes when you change gear or release accelerator and put it back on again? (can't explain it well sorry), it did this and then the warning light for the control system for the exhaust flashed and car went into limp mode. I stopped the car switched it off and back on again and it was fine drove the rest of the way home with no misfiring and no flashing light? Does anyone have any ideas of what it could be? 

Also i was wandering if the back box could be the cause as it does sound rough? 

Cheers in advance

Potential coilpack failure, or dodgy old spark plugs