P0174 system bank 2 too lean, air filter

[coffeebob]

I got "Service Engine Soon" yesterday while driving. Pepboys pulled the P0174 system bank 2 too lean. Then I checked the geniune nissan air filters. Both were quite dirty, stuff trapped by the oily filter, and have some leaves on the filter and inside the air box. After shaking and picking out the obvious dirt, light still on. After getting gas & adding chevron injector fluid, slight still on.
But after making a coffee stop, the light went away.

I replaced the air filter not too long ago, may be 25k ago. While it got dirty and clogged so frequently. I don't recall chaning my air filters so frequent in my previous 2 cars (1990 integra, 2002 325i).

thanks.