Poor Fuel Mileage

Check intake air temperature sensor.
Check engine coolant temperature sensor.
Check barometric pressure sensor (if applicable).
Check manifold absolute pressure sensor (if applicable).
Check ignition switch.
Check throttle position sensor.
Check camshaft position sensor.
Check crankshaft position sensor.
Check power steering oil pressure switch.
Check A/C switch (if applicable).
Check park/neutral position switch (A/T).
Check heated oxygen sensor.
Check volume airflow sensor.
Check fuel pressure.
Check for MFI system malfunction.
Check for idle air control motor malfunction.
Check for fuel injector malfunction.
Check for power transistor malfunction.