Cadillac Repair: Codes P0171, P0174, P0300 -- 2001 SLS, vacuum leaks, volt ohm meter

Question
P0171 and P0174 indicate a lean condition. P0300 indicates misfire.  Fuel pressure at the rail is 38 psi.  Book says 41-47 psi.  Idle engine vacuum starts at 16 and goes to 12. No apparent vacuum leaks.  Engine runs rough at idle but smoothes out at 1500 RPM. Fuel filter has not been replaced.  Car has 65K miles.  Well maintained.  Just started to have problems.  A check against a 2000 STS showed fuel pressure 38, vacuum steady at 16, no codes set.  Based on your experience, do you think this is a fuel pump problem?  If so, the STS also has low fuel pressure so why the difference?

Answer
It is possible that your gage is faulty.

If you are mechanicaly inclined or know of someone who is, You will need a DIGITAL VOLT/OHM METER, Simple electrical schematics, Test procedures and picture locations of the components within the system that is causing you problems of which can't be done on this website which only allows one picture. I do not have a website so you will have to e-mail: onlineautohelp@msn.com in order to obtain the information necessary to fix your vehicle.