Yesterday I developed a *big* stutter (almost complete engine cutout) when hitting 70mph in 3rd in my E6 GSR (happily exceeds 80mph in that gear normally). Happened twice then reset ECU this morning and was fine again until car got warm then came in big time again. No noticeable external noises though felt like a big backfire when it came in. It really is different to either rev limiter or fuel cut and I am dead worried that there was something up with the SUL I put in it yesterday. It was fine before this but developed the problem afterwards - is there such a thing as 'dirty petrol' which could effect things? I'll get it MUT tested Tuesday but anyone got a lcue please? TIA.