Will the idle not drop if you adjust the idle adjuster?
Did you reset the ECU? It is a learning ECU.
Did you check the fuel line pressure? Should be 47PsiWhen you tested the items did you check the wiring connection back to the ECU? Did you check the Multi point earth which is prone to corrosion?Was the fast idle included with the replacement throttle bodies, is it adjusted properly and is a common source of high idle issues. Has the TPS been set correctly?Did you try disconecting the O2 sensor?
The symptoms are suggesting issues with the cold start circuit. There are several sensor the ECU uses to control that circuit. You state you've tested them, try disconnecting the temperature sensors one at a time see if you can get the revs to drop to 1200. Test fuel pump pressure, you'll need a gauge for that. Also check the fuel return circuit ie blocked or restricted. Check the air box for restrictions or damage eg holes/splits. Look for signs of a boost plug these are plugged into air temperature sensor in the intake, these fail overtime. Some are home made bodge jobs and cut into the loom, only to be removed on selling. The std sensor will test ok, but if the loom is damage the circuit won't work correctly. Check the loom for signs of an alarm having been removed or fitted incorrectly.From what you've stated, over fueling is your issue, but the problem may well not sit n the fueling circuit. But rather one of the supporting circuits.