Pontiac Repair: check engine light, vacuum leak, vacuum lines

Question
'97 Bonneville SE/117,000 mi. Car runs great, never a problem, but, cannot kill 'check engine' light, cannot get inspection, P0171 code comes back. Replaced both O2 sensors, MAF sensor, vacuum-lines. Erasing the code works for the same day. Next day it comes back again. Thanks !

Answer
Hi Charles:

Did this just crop up out of the blue or did it occure after some sort of engine repair? the 171 code is a lean condition code it can be set by a number of things. a MAF sensor out of range, A internal vacuum leak namely around the pcv valve there is an o-ring under it and if that wasn't transfered when the valve was replaced it will cause the code. you could have low fule pressure either from a bad pump restricted fule filter or a bad pressurre regulator. I think this engine needs between 42-46 psi pressure with the key on engine not running and when it's running it should drop back a few pounds. without a scan tool this is a really hard code to find. if you had one where you could see the fuel trim readings it makes it much easier to find the problem. Just a few things to check. Good luck :}