First, make sure your battery voltage is within spec. Low voltages can cause all sorts of faulty code generation. Second, verify the condition of the fuses in the Base Module. Have you tried clearing the codes and seeing if new codes are generated? One problem that many MB's suffer from is deteriorating wire insulation. The insulation in my MAF harness and within the passenger side Electronic Throttle Actuator was cracked and falling off. This caused Check Engine lights, surging at idle, etc. Check out my web page for details and what to look for. Click on the link below my signature. Also, JimF's web page is full of good info, and it relates specifically to your engine.
http://pages.prodigy.net/jforgione/MB_asr.html