Shall be tinkering with the car tonight or tomorrow night. Handbrake adjustment, some flyeye action and a tidy up.
Also will go over the bay and double-check for any split hoses, etc. Boost gauge is reading correct on idle (i think lol) like -0.7 bar and is boosting too around 1.2 bar under load. So I'm just guessing here, but I don't think there is a boost leak and that a leak is the causing the misfire.
I do remember now it started to appear when I used octane booster with 99 octane fuel. Now I'm thinking could it be the O2 sensor? But surely that would cause running issues regardless of boost?
Its runs fine with the boost turned down and with the boost up its fine just doesn't like when its under load. The vid of my burnout attempt shows it a little. 1st gear, I have no problems, then when I shift into 2nd during the burnout it misfires due to the extra load on the engine.
So it misfires (badly) under load when it hits full boost..... Other things I should try I guess would be DV and N75.