my friend changed his radiator and a little after that his engine would idle hight when it was cold really hight then when he is on the gas for a while it goes back up when it is warm

 

Tell him to bleed his cooling system some more. Make sure the heater control is all the way to 'hot' because air bubles like to hang out in the heater core.

Whan an air pocket gets to the FITV it can make the idle speed go up. When an air pocket gets to the ECT sensor it gives a bogus measurement to the ECM.