P0174 - bank 2 running lean...

Two months ago I had the car serviced for P0174 and P0171 codes, which they traced to the air filter that had been eaten away by a mouse. They replaced the air filter, and cleared the code. No trouble for 100-150 miles or so. Now P0174 comes up, and I want to get some ideas before I go to the dealer, from what I've heard it can range from a vacuum leak to a dirty MAF to bad O2 sensors. I wanted to know what to start with first, as I don't want to have the dealer waste my time or money in case they misdiagnose it, considering this code can be caused by a variety of things. 60,000 miles, 2004 X3 3.0i.

Any advice would be greatly appreciated.