Hi guys,
Ive got a 53 999 which has just started back firing when it's ticking over

. It's fitted with a RaceFit exhaust on the standard ECU and front link pipe (with CAT) but has been running fine for over two years.
I have looked at a past threads on here (loose air box gasget etc), I've been told that it could possibly be the front coil pack breaking down or my RPM/Timing sensor.
Can anyone offer any other reasons/advice - cheers