The correct idle speed for a 2001 Ford F-150 with a 4.2L engine and manual transmission isn't a single, universally stated number. It varies slightly depending on engine temperature and other factors. However, a generally accepted range is
650-750 RPM.
You should consult your owner's manual for the most accurate information specific to your vehicle. The manual will often give a range and specify whether the engine should be at operating temperature for the reading.
