Why does the engine idle roughly during cold starts?
2 Answers
The reasons for rough idling during cold starts are: 1. Faulty coolant temperature sensor: If the engine temperature is -10°C during a cold start, but the sensor reports 10°C to the ECU, the ECU will inject fuel based on the 10°C condition, resulting in insufficient fuel supply and natural shaking. 2. Engine carbon buildup: Carbon deposits can lead to reduced fuel injection, failing to ensure adequate power output, inevitably causing shaking. 3. Aging vehicle: If the car has been used for many years, components nearing the end of their service life may produce shaking. 4. Insufficient ignition energy: During cold conditions, the temperatures inside the engine, fuel, and lubricants are all low, requiring more fuel injection during cold starts to meet power demands. Larger spark plug gaps result in weaker ignition energy. Poor fuel atomization at low temperatures demands higher ignition energy. Prolonged use can enlarge spark plug gaps, reducing ignition energy and affecting power output, leading to shaking. Additionally, aging ignition coils, deteriorated spark plug high-voltage wires, or electrical leaks can also decrease ignition energy.
As a car owner with fifteen years of driving experience, I often encounter the issue of engine shaking during cold starts. The most likely causes are aging spark plugs or carbon buildup—worn-out spark plugs can lead to unstable ignition in cold weather, resulting in irregular operation of certain cylinders; carbon deposits mainly accumulate on the throttle body and fuel injectors, affecting the fuel-air mixture ratio and causing uneven engine combustion. Additionally, cold engine oil has higher viscosity, and if the oil is too old or of the wrong grade, insufficient lubrication can increase friction-induced vibrations. Sometimes, faulty sensors like the coolant temperature sensor can cause the ECU to incorrectly adjust the air-fuel mixture. I recommend that owners warm up the engine for a few minutes first and observe—if the idle stabilizes, the issue may not be urgent. However, if the shaking persists, promptly check the spark plugs and clean the fuel system. Regular maintenance is key: clean the intake tract every two years and choose the appropriate oil grade for the season. Ignoring this problem could lead to ignition system damage, and driving safety is paramount.
