Have you read the TPS setting instructions from commanderjjones, it is a sticky at the top of the Ranger technical page.
Are you the original owner? It sounds like to me that someone has tried to adjust the idle screw, which is not allowing an accurate reading from the TPS, because of the throttle plate position.
Have you cleaned the TPS, make sure you use a cleaner that does not leave a residue (brake cleaner, throttle body cleaner).
Also check that the throttle plate is not catching on the throttle body housing, you can see the wear marks.
Are you the original owner? It sounds like to me that someone has tried to adjust the idle screw, which is not allowing an accurate reading from the TPS, because of the throttle plate position.
Have you cleaned the TPS, make sure you use a cleaner that does not leave a residue (brake cleaner, throttle body cleaner).
Also check that the throttle plate is not catching on the throttle body housing, you can see the wear marks.