Is it normal for the engine to jerk when starting?
3 Answers
It is normal for the engine to jerk when starting, as cold starts often cause vibrations. The reasons for vibrations during a cold start are as follows: Low ignition energy: Low ignition energy leads to engine vibrations. When the engine temperature is too low, both fuel and lubricant temperatures are low. During a cold start, a richer air-fuel mixture is required, which in turn demands higher ignition energy. Excessive spark plug gap, aging ignition coils, or high-voltage coils can all result in reduced ignition energy, causing the vehicle to shake. Incorrect air-fuel mixture ratio: An incorrect air-fuel mixture ratio can cause vibrations. During a cold start, certain engine sensors or sensor signals may have significant errors, leading to ECU miscalculations. This can result in inaccuracies in fuel injection timing and ignition timing control, causing the engine to vibrate.
I usually enjoy studying cars, and this issue is quite common. When starting the engine, a sudden jerk is often abnormal. This could be due to a problem with the starter motor, such as misalignment between the motor gear and the engine flywheel, causing a jolt during startup. It might also be caused by insufficient battery power, where voltage fluctuations affect the ignition system. Another possibility is aging ignition coils or spark plugs, leading to rough ignition. A slight one-time jerk during cold starts might be normal because the engine oil is still thick, requiring more force to start the engine. However, if this happens every time, the risk increases significantly. I've experienced this myself—I immediately checked the battery voltage; if it's below 12V, it's dangerous, and the battery needs replacement or charging. Additionally, inspect the electrical connections in the starting system, as loose wires can cause unstable startups. Modern cars have complex electronic systems, and a minor fault can trigger a chain reaction. It's best to have a professional technician diagnose it with a scanner rather than waiting for a breakdown to occur.
Having driven for nearly 20 years, I'm quite sensitive to engine abnormalities. Your situation sounds like the engine jerks violently during startup, which is mostly abnormal. I remember my old car had the same issue, and it turned out to be a worn starter motor with burnt relay contacts causing uneven rotation; another common cause is an aging battery with reduced capacity and insufficient starting current. Minor shaking is understandable in cold weather or right after washing the car, but if it jerks severely every time, you should be alert—it could damage engine components or even lead to a breakdown. My lesson is not to skimp on repairs: take it to a repair shop immediately for a system test. Usually, replacing the battery or starter components will solve the problem. Regular maintenance is crucial; checking the starting system every six months can greatly prevent such issues.
