Yesterday finally got a chance from my busy schedule to replace the spark plugs with Denso Iridium. Surprisingly, when I scanned and cleaned the throttle body from my mechanic last month he didnt tell me to replace the plugs as they were quite brown on the tip. Now the car is become much smoother and I can feel the difference in driving.
However, the stuttering sounds after starting the car still remains for few seconds as I noticed this morning after the car was parked overnight. Only happens after car is parked for long durations. Next will now check the battery for any problems.