2001 Cadillac Deville system to lean

P0171/P0174

A lean fuel condition can be caused by:

* Low fuel pressure due to a weak pump or leaky fuel pressure regulator. (use a fuel pressure gauge to check fuel pressure at idle)

* Dirty fuel injectors. (try cleaning the injectors)

* Vacuum leaks at the intake manifold, vacuum hose connections or throttle body. (Use a vacuum gauge to check for low intake vacuum)

* Leaky EGR valve. (Check operation of EGR valve)

* Leaky PCV Valve or hose. (Check valve and hose connections)

* Dirty or defective Mass Airflow Sensor (MAF). (Try cleaning the MAF sensor wires or filament with aerosol electronics cleaner. Do NOT use anything else to clean the sensor, and do not touch the sensor wires)

i just replaced the spark plugs could a faulty plug or not tourqing the right pounds of pressure for tightning the plugs can cause it to say system to lean banks 1,2 P0171,P0174

That would cause an ignition misfire-why don't you check it. A lean condition is where the air/fuel mixture has more air than fuel during combustion.

Check for a split boot between the intake manifold, and throttle body. It usually splits down on the lower portion of it, and is a very common cause of this symptom.