2003 Ford Fairmont • 6 cylinder 2WD Automatic • 125,000 miles

My 2003 Ford Fairmont engine stumbles and hesitates when the air conditioning is running. It is worse using standard unleaded and reduces on high octane unleaded. Is this electrical or fuel line related? The car is designed for standard unleaded. It also hesitates and stumbles when accelerating briskly. Under light throttle this does not occur.
February 20, 2011.

Lack of acceleration, chugging, hesitating********, bogging, misfiring etc. Could be caused by one of the following below

Oxygen sensor.
Catalytic converter.
Fuel injectors dirty/sticking.
Mass airflow sensor/Airflow meter.
Throttle position sensor.
Crankshaft position sensor
Knock sensor
Manifold absolute pressure sensor.
EGR Valve
Fuel pressure regulator leaking or defective fuel pump.
Fuel contamination.
Foul/defective spark plugs.
Open spark plug wires.
Ignition coil/Coil packs defective.
Incorrect ignition timing.
Cap and rotor.

Note: If it doesn't apply disregard it and keep testing.

Feb 20, 2011.