what is P1506 because the engine light is on. on 2001 Ford Escape

The engine light stays on and when placed on the diagnostic scanner, the code P1506 comes up.

Asked by for the 2001 Ford Escape
This code indicates that the engine speed is greater than the engine's computer is calling for. The causes could be a defective Idle Air Control (IAC) Valve, a vacuum leak, or a wiring issue related to the IAC valve.