I thinking to do a top over haul on my engine, cos the lower gasket has lived it's time and needs to be replaced. I say this cos I can see oil stains on the lower gasket part. And when I remove my spark plugs, there screw threads has got a bit of oil on them. So from there, I'm guessing that my lower gasket is KO already.
Also, the other day, my car was jerking really really bad. Then I turn off the engine, wait about 5 minutes and start it back, the problem was gone.