Look for a vacuum leak...
Code P1506 - Idle air control valve over speed error
Idle air control over speed
Well I found out the answer on my own.................thank you very much! It turns out it was the pcv valveon my vechile. Another thing that can cause it would be your (IAC Valve) aka idle air control valve or it could be a engine vaccum leak. Good luck.
bad vehicle speed sensor
i have a problem with the automatic climate control the fan has only high speed
It is aturbine\speed sensor malfunction. It usually means that this speed sensor has gone bad. Good luck.
In a 1997 Ford Explorer : Control Trac is Fords name for the 4x4 system , with the 2 speed transfer case ( it has a LOW RANGE that can be used off-road )
The idle speed is controlled by the powertrain control module ( computer )
The powertrain control module limits the RPM of the engine by cutting back on the amount of fuel to protect the engine
If you are refering to the OBD-II code 791 or P0791 it is refering to the Intermidiate Shaft Speed Sensor Circut A.
It has to do with the speed control vacuum circuit in the cruise servo.
You may need to repair the control speed board. It's a classic fail.