Thanks for the input Court X3! Intake valve cleaning is another option via the thread #10.
I will try to remove intake manifold to clean and replace intake gasket as well.

However, today i test the engine: Whenever i insert key knob and turn the ignition on (not start the engine yet) and leave it for 5 seconds and turn on the engine, the jerk/shaking and moving rpm needle up and down disappear -> engine start normal.

It only happens when i insert key knob and turn on the engine right away.

This makes me think about the low fuel pressure due to in-tank fuel pump issue.

How do you think?