Code P0430 and Engine Stumbles When Accelerating

[X5Cat]

I was steered to the Veepeak adapter and OBDFusion app four years ago by jfoj, on this site. Seems to work pretty well with my iPhone. Don't remember if it knows BMW-specific codes, but as long as it just reads them, I can look them up on the interweb. I remember it gives fuel trim data, temperatures, barometric pressure, rpm, throttle position, fuel rate, calculated load, MAF rate, timing degrees, O2 sensor voltage, and all that jazz, so maybe there will be something there to gives some clues for the diagnosis.