Richard, the misfire you are having has similarities to what I suffered with my GDI, and sadly I never got to the bottom of it. It came on first on an uphill stretch, and all power vanished, but it would start and idle perfectly. It never went into limp mode. After some throttle pumping it would rev to the limiter in bursts, and then stutter back to a steady tickover. It did this about six times on that journey, in which I filled the tank. It felt like water in the fuel (and may have been) or an electrical glitch. By the time we got home, it was running normally. There were no error codes. I changed the relays, and checked the fuses, and because the tailpipe was blacker, decided to replace the cat, and sensors as emissions were rubbish anyway. So it remains an enigma.

DaveW
'05 Red Roadster S1
'16 Yellow (Not the only) Narrow AR GDI Plus 4