Yaar try not to fiddle with RPM of 5AFE. There is no RPM adjustment in this engine so you should have kept it stock.
When the engine is cold RPM will raise to 1200 or 1400 as soon as the engine get to normal working temp it will go down to normal RPM.
If its taking 10 to 15 Mins check if you have thermostate installed. With thermostate within 2 to 5 mins RPM comes down to Normal.
At Idle your RPM should be around 800 to 900.