Ok, back from running the car with and without AC to see the idle rpm. See the snap
Unfortunately, while I was taking the snap, the torq app wasnt logging. But you can see the 550rpm dip. I took other snaps also where the idle is just about 600.
A screen shot of the OBD output shows that the lowest speed is 600~620 rpm. Also note that the rpm peaks every 20 seconds and then decays slowly. And the lowest dip is just before the peak. This is as if the system follows a sawtooth curve. There were drops to 600rpm or so in the obd output but somehow, that image didnt get sent.
Without aircon, the car idles consistently between 620 and 660rpm and doesnt dip at all
So when the car is at minimum rpm and this coincides with engine loading such as clutch release or such, things like stalling and headlight dimming occur
Running the fan in auto mode helps for a moment but the rpm drops back again. In fact I have been hearing the fans speed going up and down depending on the engine rpm all the time
Ameyam