retarded = more heat.

think about the way the engine works with valves opening and closing and youll see why, as youre making your burn occur later in the cycle so more heat is getting let out of the exhaust valve.

for idle dont worry too much about giving it some ignition, youre not going to melt the engine ticking over.

have you got a baseap to work off of? even if its another ECU and you can manually copy the map?