1990 Range Rover when engine is hot the revs will not drop below 1700. Engine has been tuned and a replacement ECU fitted. Help

 

Sounds like your stepper motor or IAC, whatever they call them on your year and model, is dirty/carboned up. This is what is responsible for your idle control.
Also you want to look for vacuum lines that are leaking.
Mike

 

Mike, thanks I will try cleaning and checking its operation