The air regulator is under the inlet mainifold mounted to the bottom of the throttle bodies.
It has 2 pipes on it one either side all you need to do is crimp one up to block it with a pair of plyers or molegrips.
you may find it easier doing this from underneith. it can be a basta*d.
Here is the description of the air regulator as per Nissan manuals.
Air regulator
The air regulator provides an air by-pass when the engine is cold for the fast idle during warm up.
A bimetal, heater and rotary shutter are built into the air regulator. When the bimetal temperature is low, the air by-pass port opens, As the engine starts and electric current flows through the heater, the bimaetal begins to turn the shutter to close the by-pass port. the air passage remains closed until the engine stops and the bimetal temperature drops.
I think the air regulator is staying open giving you all fast idle all the time.
By blocking the air regulator pipes you are basicly turning off the fast idle.
Give it a try and let me know how you all get on.