Volvo: Volvo engine code, fuel air mixture, mass air flow

Question
I have a 1996 volvo 850 turbo.  I am getting a P0171(engine too lean bank 1)code every 60 miles. I have checked for air and vacume leaks to no avail.  What else should I look for?

Answer
Bruce,
Look for these 2-3-1/P0171 LONG TERM FUEL TRIM PARTIAL LOAD

Precondition for DTC


The control module receives information from the Heated Oxygen Sensor (HO2S ) about the fuel/air mixture in the idling and partial load ranges. If the fuel/air mixture deviates from Lambda=1 the short term fuel trim will compensate this by adjusting the injection timing so that Lambda=1 is achieved. When the short term fuel trim carries out this adjustment, its mid-point must be adapted by the long term trim. When the long term fuel trim has adapted the short term trim to a maximum value, DTC 2-3-2 (idling range -0.48 ms to +0.40 ms) or DTC 2-3-1 (partial load range 0.773 to 1.227) and status message Upper Limit (lean fuel/air mixture) or Lower Limit (rich fuel/air mixture) will be set.
Substitute values.


Upper limit:
Defective Mass Air Flow (MAF ) sensor.
Low fuel pressure.
Air leakage.
Faulty sensor signals.
Lower limit:
Defective Mass Air Flow (MAF ) sensor.
Air leakage.
High fuel pressure.
Leaking injectors.
Leaking EVAP system.
Dirty engine oil.
Oil level too high.
Faulty sensor signals.