Carbon deposits are sticky black residues from incomplete combustion of fuel and oil. They build up on the throttle, injectors, intake valves and pistons.
Symptoms include rough idle, hard cold start, weak acceleration, higher fuel consumption and unstable idling.
Effective cleaning methods:
  • Clean the throttle body
  • Clean fuel injectors
  • Walnut blasting for intake valves
  • Replace old spark plugs
Avoid frequent chemical flush treatments that may damage sensors.
Prevention is better than cleaning: use quality fuel, avoid prolonged low-speed driving, occasionally rev the engine on the highway, and maintain regularly.
Check carbon buildup every 20,000–40,000 km.