Okay so here it is:
Tappets - Got them adjusted many times... No difference in performance noted
Spark plugs - Replaced 2 times - NGK Spark Plugs - No difference in performance
Ignition wires - Got them checked but didn't replace them. Mechanics say they seem okay!
Fuel injectors - Got them serviced and cleaned 3+ times
Ignition Coil - This seems to be working fine. Current is very strong
Fuel filter & Fuel Pump - Mechanic says that petrol is coming without any hindrance so these should be okay. Otherwise car should show some delay in startup. Startup is very quick so they must be okay. There is a continuous siren type noise from fuel Pump though. But mechanic still says that fuel pressure seems okay so no need to change fuel pump to do useless expense...!