I see you're on the Benzworld forum, as well. I responded there to your last e-mail there. I'll just cut and paste: If anything, find out how much the ECU costs as that is the one thing I can't test.

That's misinformation. The diagnostic module is not married to the car. The ECU's starting in 1996 were. I know this because I have access to a 1994 C280. I switched out the diagnostic module as the dealer said they thought it was the diag module. Must be their default answer. Anyways, I switched out the diag modules between the 2 cars and the 94 ran all the monitors (with my diag module) while mine ran into the same 3 not completing with the 94 diag module. I also know from technical sources, that it was the ECU's that were coded starting in 1996. Sure enough the 94 ECU in my 96 would not allow the car to start. It may be the ECU but I'm not going to spend several thousand on a module that can't be returned or resold. After 5 starts, a new ECU gets married to the car (really the ECU to the starter module, so if you find the pair I suppose from the junkyard, you could test it.) All I know for sure is, that the secondary air is not running the second time. Does your secondary air run after the car has warmed up? I'm sure MB has a regional technician that knows the in and outs of the OBDII crap they designed. I'm pretty sure I know more than the dealer techs at this point. I know I don't have all the tools, as well. Please keep me updated.