So a little update on my situation (its been a long story, I will try to summarise):
1) The initial cause of the HT lead becoming disconnected was that the spark plug end/terminal had become loose with the vibration of the engine. I didn’t know these were removable. Check yours are still tight (they screw on)!
2) The resulting explosion of unburnt fuel in the exhaust caused a small metallic filter which is located in front of the lambda sensor (2012 car with a 2017 sports exhaust) to disintegrate and block the silencer. Thus why it still drove and power was ok, but the noise was strange.
3) The car is currently at the dealer. Since they have no parts and the factory is shut, they will try running the car without the filter tomorrow and see if the Lambda sensor or ECU throws up any faults. The alternative seems to be a replacement exhaust manifold (getting expensive!)
Does anyone recognise the filter in question and do you know what it is for – e.g. protecting the lambda sensor from heat, just noise etc?
