There isn't a single answer to your question about set-up/tuning. The problem is that you undoubtably have an aftermarket lambda control system or other systems added to meet US emissions when the car was imported.
Typical euro cars won't have any fuel control measurements at the diagnostic connector only component fault codes. Actually I'm not even sure which system the car would come with. I presume it still is plain K-jet not K-Jet w/lamda or KE-Jet. This will need to be determined to answer your question. If you get me the Bosch number for the fuel distributor I can determine this answer.
I have seen two different methods for "federalizing" these cars. One was to add a lambda system by adding a frequency valve to affect the control pressure (this was very tempermental as the control pressure has too great an effect on mixture.
The second method was even cruder. It involved a catalyst and air injection pump (a pre-lambda system for factory cars). The cars were clean enough that some tricky timing and mixture adjustments could get them through the testing. The timing was usually retarded to handle the NOX problem which made the car perform poorly. Most of these systems were deactivated somewhere along the line to get the running again.
Aside from fuel system monitoring the basic way to adjust the mixture is to use an exhaust gas analizer. If the catalyst is good then this really needs to be done in front of the cat. MB didn't make any provision for this as the factory cars either had no catalysts or they did and were monitored electrically at the diagnostic socket. The pin for monitoring is #3. If there is a connector beneath the hole the car must have come with K-Jet with lambda or KE-Jet.
Owner 24 bay BSC
Bosch Master, ASE master L1
26 years MB technician