If the overdrive is flashing, read out the OBD2 codes with a scanner that can read Ford transmission codes. What year is your truck and what year is the replacement engine and what is it out of? Do you have a 4R70W or a E4OD/4R100 transmission?

 

 

 

Try an auto parts store, they generally will read codes free, some of their scanners may be able to read manufacturer-specific codes. Repair shops and transmission shops can definitely read them, for a fee.

 

High idle is the IAC is open and not being controlled by the computer. It's letting air in the same as your foot on the gas pedal would.
The shift issue sounds like wires have been pinched , grounded , crossed, shorted when the transmission work was done. May even be a blown fuse #23 along with it.
Why did you accept the job that way?

 

 

Fuse is in the engine bay box.
If blown, a short to ground has or exists.
This would come from the harness under the truck that feeds the transmission solenoids, Ox Sensors and EVAP fuel system at the gas tank.
You will need to get under the truck and check this all out.
It would all be physically involved with a trans change.
Good luck.

 

 

 

 

The codes tell the whole story.
Both rear Ox sensors circuits are open. A harness or plugup issue. Get under and look.

Trans range select plugup issue. computer can't see the shift positions.
Trans Torque converter circuit.
Trans Solenoid B .
Electric pressure control solenoid (EPC) in the trans is shorted. According to the code 1747. Without this the truck cannot move very much with no fluid pressure to work with..
.
Your friend did not get the harness and plugs in place and is damaged as I suspected..
Get this all straightened out and everything should work.
Fuse 23 feeds power to all these parts.
If it is not blown, the harness is likely cut open to the point the circuits are open toward the fuse.
The codes are set because the computer monitors all the circuits, able to tell the condition and set the codes.
That's why there are diagnostics built in the program.
No use to ask any more questions but time to get under and fix it.
I gave you enough info to work from.
Good luck.,

 

 

 

Get the truck up high enough to get under safely.
The harness comes down the rear of the passenger side of the motor.
Goes to the driver side of the transmission to a plug.
It also connects to all 4 oxygen sensors and goes back to the fuel tank area. One each side just below the exhaust manifold outlets to the head pipes. One each side in the middle of the rear Cats.
Look up front where the transmission goes against the engine block for wires caught between.
Look. over the rest of the harness for issues.
I suspect the idle issue is a secondary result of the harness issue so you have to clear the trans issue first to see.
If you can't do this get a shop and tell them what to look for and why.
Good luck.