My problem started 5 months ago when I stepped on the gas and my power suddenly decreased. Then my "Engine Check Light" came on. Every time I stepped on the gas, it seemed like the Kompressor was not engaging (decreased power). I took the advise from "Ethan" and John S and purchased a hand held scanner. I hooked up the hand scanner and got the following codes:
P1420 - Air Pump Switchover Valve
P1235 - Camshaft Positioning Sensor
P1525 - Adjustable Camshaft Timing Solenoid

My MB dealer replaced my "Air Injection Valve" at the Kompressor. This took care of the problem for about 5 months and then the same thing happened. I decided not to pay MB $1200 again (only to have the problem reappear), so I went to the “AllData” (http://www.alldata.com/products/diy/) web site and subscribed for one year ($14.95). The web site provided me with the proper Diagnostic Trouble Codes, Specifications, Diagrams, Troubleshooting charts, etc. Everything pointed to the Air Pump Switchover Valve. So, I replaced the "Air Pump Switchover Valve", because that was the first code that came up. Well, I ran the scan again and received the same codes. I shouldn't have gotten the same code for the "Air Pump Switchover Valve" because I just changed it. So, I looked at a MB trouble shooting chart and it said to test the K40 relay. I don't have the special 128-pin test box, so I took the cover off the diagnostic box (upper left hand corner, if you're standing in front of car) and took out the "Relay Module" box. Mostly all of the relays are contained in this box and soldered to a circuit board. Then I had to open it up and find were the K40 Relay was on the circuit board. Wasn't hard to find because there were two BAD solder joints for the K40. I re-soldered the connections and I haven't had a problem since.
Maybe this might help anyone that is having the same problems that I had.
Carl