First some details about my setup - its in an mx5 based kit car I'm building not actual mx5.
diy MS2 running diypnp turbo basemap (afr and spark) ran autotune VE at idle and moderate driving but no WOT yet.
No IAC valve
TD04 turbo on diy manifold with small intercooler
380cc yellow rx8 injectors
AEM wideband (setup as custom linear wideband)
Starts ok from cold and runs a little rough as expected with no IAC valve but after a minute or so it idles quite nicely. When it gets up to full temperature it splutters and missfires a lot (once per second) although still maintains a reasonable idle (900rpm +/-30). AFR of 13 although the needle fluctuates. If I give it some revs it continues to splutter under no load but when actually driven in gear it doesn't. It drives ok - leans out on sudden acceleration but I want to get idle sorted before I worry about that.
Anyway I've tried giving it more or less fuel around idle and advancing and retarding the spark and none seem to improve it which leads me to believe that it might be issue with setup or even hardware (coils dodgy when hot?).
Other thought was I have a v band on the downpipe upstream of the wideband sensor and perhaps these don't form a perfect seal leading to false readings? Here is a pic of the setup. Ignore the tiny air filter - that was just to keep the dust out while building and has been replaced with proper one Note that I haven't finished the exhaust beyond the downpipe.