[Melto]

Usually if the fan keep on running at high speed after you kill the engine, there is a problem sent to the ecu.
Better have it scan and see what code it pops out. Since you already changed the plugs, did you also check on the coils?

 

[Melto]

Hey, yeah, i got it checked and it displays p1336 - refering to a cylinder misfire. The garage guy said he wont be able to tell which cylinder fired though, any workaround that? I don't wanna replace all of them

Your mechanic should be able to list out which cylinder is having problem. He just have to click on the issue code and expand from there.
Here is mine: for reference

 

[Melto]

Went to the mechanic again, he showed me the code, but mine doesn't list the cylinder. only a generic p1336 error. Booked in to get a combustion test (since car is under warranty], hopefully that brings something up. Thanks for the help, did it resolve after getting a new cylinder?

Didn't require a new cylinder, changed the firing coil which is cracked and the code when away. (also the timing solenoid and plugs for the other codes)
Now no more engine management code, but when I rev it hard above 4k, it gives a spluttering or popping sound, mechanic says it not misfiring but could be due to the catalytic converter or a cracked exhaust piping. Have not fix the issue yet, no hurry cos the sound only comes out when I rev it real hard, daily drive is still good.