Q: My 07 explorer 4.0L hesitates and hums when I'm on the gas pedal, but I can accelerate smoothly and quietly using cruise control.

The noise and loss of power may or may not be related. The vibration might be related to the poor operation but other causes such as faults in motor mounts can cause vibration not to mention a faulty harmonic balancer. If engine cylinder compression has become uneven, that can cause vibration. Cruise control and manual operation of the pedal both use the throttle position sensor and, in any event, the throttle position sensor is easily tested using a real time automotive scanner. With 220,000 miles, among my first suspicions would be partially blocked fuel injectors. You can indirectly get an indication of that by looking at short term and long term fuel trims on the real time scanner. Another cause of poor acceleration is inadequate fuel pressure/volume. A defective fuel pump will not supply enough fuel to the injectors. This can cause the vehicle to hesitate or accelerate slowly. A dirty mass airflow sensor can cause the wrong data to be be sent to the computer. A slow accelerating car is the result of this incorrect data. Other causes of poor acceleration are vacuum leaks, ignition system faults (old plugs for instance) and a defective idle air control valve. To get the underlying cause of the problem pinpointed and resolved, you can request an engine diagnostic for slow acceleration and the responding certified mechanic will get this taken care of for you. If you have further questions or concerns, do not hesitate to re-contact YourMechanic as we are always here to help you.