Thank you for the detailed reply.
For oil, i'll probably opt for Toyota 5W-30 or Total Quartz 9000 5W-30, as i have been using these 2 oils in my altis for past 2 years and their performance is satisfactory as compared to Toyota 10W-30.
I am apprehensive about throttle body service, since I am yet to come across some one who can properly service the throttle body in LHR.
I have already had a bad experience with Honda 3S mechanics for servicing the throttle body as they screwed my idle sensor calibration and I had to re-adjust it myself.
Since the car idles rough even in N mode, and the roughness intensifies when i turn on the lights.
However, what I have noticed is that when i came to a halt after 30mins of continuous driving, the roughness wasn't there any more, perhaps the battery got charged?