I'm planning on replacing the oil sensor tomorrow and using 15w-40 oil hoping it will go away.

At this moment hte light will flicker occasionally for less than a second when in drive at a stop light.

If its in part it wont flicker etc I raised the idle but it still does it because it still idles at 600 in drive with the brake pressed.

Is this a sign the oil pump is going bad?

I've never had this problem before and should i just brace myself so i can replace the oil pump or is the flicker something else?

I've been using 10w-30 lately

The oil light only starts to flicker ocne the car is upto temperature or usually after an hours drive sometimes it takes longer today after about 3 hours driving it would flicker at every time the idle went below 900rpm.

Otherwise it doesn't come on

The oil pressure switch is a common casue of this problem. Just change it and see what happens. You probably won't even need to switch to 15w40.