Long time no update liao, here's some update, good info in case you guys encounter the same problem.
After the GB dissection, my water temp gauge became unreliable. When the compressor kicks in, the water temp will go up, and when the compressor turns off the temp will go down immediately, confirmed from the ECU reading that the engine is not overheating. Changed the temp sender for the gauge and problem still same. Mech suggested to check my grounding and I just gave the grounding cable and mounting points on the chassis some grinding, and also added another grounding cable as well while I was at it, and the temp sender started working like normal again
Also another problem was recently I noticed idling was rougher than usual and town driving is just pretty horrible at really low RPM where the engine can get really jerky. Thought it was my tuning problem but no matter what I do I just couldn't tune it out. Wanted to play around with the cam timing to reduce the overlap, opened the timing belt cover and, lo and behold, the intake cam had move itself all the way to one extreme. Somehow the 5 allen bolts holding the cam gear down wasn't torqued properly and required very light force to get it to loosen.
Although the cam markings shows that it is full Retard, it is actually at full Advance. The markings on the cams are reversed. With the intake cam fully advanced, the valve overlap is alot more, and I was pretty lucky the valve did not kiss the piston!
The cam gear had moved 8 markings on the gear, 1 marking representing 2 crank degrees. The cam had advanced a whole 16 degrees!
Adjusted it back and give it slightly more retard this time, and idling was smoother with more vacuum and driving around town is soooo much smoother now with no jerky jerky.