What Causes Engine Shaking During Cold Starts?
2 Answers
Engine shaking during cold starts can be attributed to the following reasons: 1. Incorrect air-fuel mixture ratio, where the fuel-air mixture is improperly calibrated, occurring in both open-loop and closed-loop control systems. In vehicles with closed-loop control, the oxygen sensor operates at 370 degrees Celsius; 2. Carbon buildup on valves and intake ports. If carbon deposits form on the engine's valves and intake ports, they can absorb a certain amount of fuel, leading to incorrect ECU judgments; 3. Uneven cylinder conditions. After prolonged engine use, the clearance between each cylinder liner and piston may vary, with larger clearances allowing some high-temperature gases to leak, reducing power output; 4. Faulty coolant temperature sensor. If the engine starts at -10 degrees Celsius but the sensor reports 20 degrees Celsius to the ECU, the ECU will inject fuel based on 20-degree conditions, resulting in insufficient fuel and causing shaking.
I've been driving for over 20 years and have seen plenty of cases of engine shaking during cold starts. It's mostly caused by carbon buildup in the engine, especially around the throttle body. When carbon accumulates, the air-fuel mixture becomes uneven, leading to incomplete combustion during cold starts, which makes the car shake. Also, if the spark plugs aren't performing well and don't provide enough ignition energy, one of the cylinders might misfire. And if the rubber engine mounts are worn out, their damping effect is lost, allowing vibrations to transfer directly to the steering wheel. I recommend first checking for carbon deposits, cleaning the throttle body and fuel injectors, then testing the condition of the spark plugs, while also checking if the engine mounts are cracked—all of these can affect cold-start stability.
