My other car is a MINI!!!!
This might sound really daft jay, and looking back it probably is.....
A few years back I developed a misfire that I couldn't trace. The car ran perfectly when cold and warming up, but within a few minutes of reaching full temperature it'd start misfiring terribly on another over 10psi of boost.
I spent several months changing MAFs, ign amps, coilpacks, spark plugs (for new Denso IK22's), all sorts, until eventually I got chatting to the guys at Atspeed Racing in Rayleigh, I was only there with a mate and mentioned my issue, and the guy immediately said it was plugs, I explained that it couldn't be because I'd recently stuck new Densos in, and he laughed and repeated it's definitely plugs. I thought he seemed pretty rude to be honest, but he kept insisting it was plugs, so I went to the local ECP there and then and bought a set of standard plugs. Dropped them in, and the problem was gone! 100% solved.
Turns out the densos didn't suit the car and just made it all ****. Been on those ECP plugs ever since and trouble free!