P0171 Bank 1 lean.

I found this at MBWorld.org

P0171 System too lean OBD code - MBWorld.org Forums

You may have to join (not a bad thing-and free!) to view photos.

The God of MB knowledge (Buellwinkle) says:

p0131 & p0171 codes - MBWorld.org Forums

But before you start throwing cash at it, run the gas low and refill with top-tier 93 octane.

Clear the code and see if it re-appears.

Best of luck!