The carbon build up seems to be a good theory....the car had been used primarily around town, less than 10k per year by older woman owner. I've driven it hard since I got it but not under full boost until tonight.

I did try a series of accel/decel runs and could only see sparks when I lifted throttle. The quantity of sparks diminished fairly quickly after a few times.

If the car catches on fire, I can always smother it with diesel fuel, right?