Thanks all for your input.

Those familiar with M103 will know that that you can't spray water into the TB directly as access to the TB is blocked by the MAF. I unplugged the vacuum line to the Ignition Control Module and put it into water. The result is not desirable. My M103 still has some sound when accelerated brutally. I don't think it is preignition but carbon buildup on the pistons and get contact with the valves head and makes noise. Other than that, I have a moderate engine vibration at idle, the plugs look very good.

I experienced this with my motorcycle. My mechanic opened up the cylinder and made carbon buildup removed. The irritating sound was then gone.

Maybe some specialty agent is needed. I can't get seafoam over here.