Po171, po174 mean

 

They're lean codes, banks 1 and 2 respectively. Can be caused by a crapload of stuff, but the basics would be a vacuum leak, a leak in your intake some where, usually up near the maf sensor, or a messed up maf sensor. The other thing that can occasionally cause the pair to show up is a K&N filter as the airflow is quite a bit more aggressive than a stock air filter. Mine spit a p0174 today after I changed out to a visually cleaner maf, so I'm throwing the old one back in because it would seem the new one is faulty

 

simple... check the pct tube and elbows for crack or collapse

Ron