Hello,
I recently had a po171 code and posted to the list. A good member advised me of the same problem and suggested I take my 300 to the dealer that his was covered under the extended warranty. I did and it was covered. What they replaced was the Mass Flow Sensor. I had less than 50,000 miles and barely got in on the yearly time. The maf is located behind the air filter box, easy to get to. Hope this helps!
2bears