Interesting stuff Tom. I recently bought a 2001 Y body and was thinking to myself how cool it would be to have an open source tool to talk to it with. But for now I'll be dusting off my Jet cable / software (based on tunercat).

Just to clarify a few bits - the arduino IDE is not sanctioned by Atmel. They also have a free but non-open IDE suite for their AVR products but it's not quite as friendly to beginners.