Compression test is on the to-do list this weekend. When I have some extra time, I'll probably be pulling the valve cover off to take a look, unless some miracle happens.

Intake is back on and the coolant leak appears to have been fixed with the new valley pan. This seems to have taken care of a lot of the rough idle and the P0300. Carly and OBD Fusion tell me the same thing, but I need to reinstall ISTA (changed laptops recently).

I'll look into the decarbon links - thanks!