Cool.

I think I have pinpointed it to one cylinder, but I'm not sure if it's intake or exhaust. I found that even after warmed up one of the of the valves for the cylinder second closest to the firewall on the passenger side ticks, but you have to put your ear right next to the valve cover to hear it. Given that the loud tapping that initially follows cold start was coming from one of the 2 central cylinders on that side (but I couldn't pinpoint which), I'm thinking that I've found the problem.

I'll ask the guys at Abacus. It's unfortunate that there are no MB tuning shops, but happily Porsche used the same fuel injection and Abacus recommended this laptop programmable warm up regulator (controls the mixture at all times despite the name) so I'm hoping to get my tune down (right now it's WAY rich at idle and too lean for max power at full throttle...stupid vacuum-regulated mechanical fuel injection confused by my lumpy cams).