I was driving today when stopped at a traffic light with my window open noticed a sort of a whistling/air sound. My check engine light came on and I pulled the codes and they were p0171, p0101 and p0102. When my car is in park or neutral and I give it some gas it seems as if the car is going to stall out. Rpm goes down almost all the way and then kinda kicks back in?/??? At one point the RPM went down so much that the little arrow lit up on the dashboard for a quick moment and then shut off. Any suggestions on what this may be? my volvo s40 is a 2002 1.9t and I have about 85000 miles on it?

 

Check your air filter, the air filter box and hoses. Also you can check the mass air sensor.

 

Yes check the Big hoses from the Air box and the intercooler. 2 out of the 3 codes are mass flow codes.
If you hear a Hissing/air noise chances are a hose came off.