Ok, for the most people who have swapped GA15De and wondering why it is dropping RPM while turning power steering, switching on the headlights, Switching On Blower Fan, and Car not stable at idle rpm.
Here is something for you.
Usually when the uncut wiring comes with a GA15De, it has two separate grips, one holds 18 wires and one holds 5 wires. The 18 wires one is for multiple accessories relating to cabin or other functions (which i will explain later) and the five wire one is mainly the power grip, supplying +12V to most of the things.
Now, in that 5 wire grip, there is a brown wire, which directly goes to the IACV-AAC valve. I have explained about the location of the valve and its wiring in the very first post with pictures, so you can consult from there.
Now, you just have to cut that wire from that grip if in case its not already cut (brown wire) after checking the continuity between that brown wire located in the five wire grip and the one end connected at the IAC-Valve Grip itself, and you have to supply it with +12V from "ON" i.e. ignition point. Here I am attaching the reference diagram and circuit.
Now what it is and what its function:
This system automatically controls engine idle speed to a specified level. Idle speed is controlled through fine adjustment of the amount of air which bypasses the throttle valve via IACV-AAC valve. The IACV-AAC valve repeats ON/OFF operation according to the signal sent from the ECM. The camshaft position sensor detects the actual engine speed and sends a signal to the ECM. The ECM then controls the ON/OFF time of the IACV-AAC valve so that engine speed coincides with the target value memorized in ECM. The target engine speed is the lowest speed at which the engine can operate steadily. The optimum value stored in the ECM is determined by taking into consideration various engine conditions, such as during warm up, deceleration, and engine load (air conditioner, power steering and cooling fan operation).
The IACV-AAC valve is moved by ON/OFF pulses from the ECM. The longer the ON pulse, the greater the amount of air that will flow through the valve. The more air that flows through the valve, the higher the idle speed.