When I got the P0171 code I had a K&N drop-in and a Borla Hush CB on. Before taking the mods off I got the A/F sensor replaced under warranty. The car still wasn't running 100%. I took the mods off at the insistence of the dealer. It wasn't till I did remove them and went back, with the CEL still on, that they discovered it was now throwing the MAF code P0101. I found it strange that both needed to be replaced but the car's been running fine since.