Why is the car engine shaking?

[SanHarley]

Here are the reasons for car engine shaking: 1. Cylinder pressure: Low cylinder pressure. 2. Blockage: Carbon deposits and oil sludge blockage. 3. Fuel injector: Fuel injector blockage. 4. Water temperature: Abnormal water temperature. 5. High-voltage line: High-voltage line break. Below is extended information about the causes of car shaking: 1. Insufficient power: Shaking during startup is caused by insufficient fuel combustion leading to lack of power. 2. Idle issues: Idle shaking is due to severe engine carbon deposits, ignition system problems, or unstable oil pressure. 3. High-speed shaking: High-speed shaking is caused by incorrect tire pressure (too high or too low), abnormal tire wear, rim deformation, shock absorber failure, or tire imbalance. 4. Engine aging: Worn engine mounts. Engine mounts are the shock absorption system of the engine, responsible for absorbing minor vibrations during operation. If the engine mounts fail, these vibrations will be transmitted to the steering wheel and cabin, causing the car to shake.

[HectorFitz]

I've been driving for almost twenty years and have seen plenty of engine shudders. The most common causes are aging spark plugs or excessive carbon buildup, leading to uneven ignition—making the car shake like a sieve at idle. Last time my old ride was trembling, replacing all four spark plugs immediately stabilized it like Mount Tai. Fuel system issues are also frequent culprits: clogged injectors or insufficient fuel pump pressure can cause uneven fuel spray, making the engine wheeze like a bellows. If the engine mounts are cracked or worn out, even normal engine vibrations can't be contained, leaving the steering wheel shaking until your hands go numb. Don’t overlook carbon buildup either, especially in direct-injection engines—thick carbon deposits on the back of the valves restrict airflow, making the engine shudder like it's starved for oxygen. Check these areas promptly—clean or replace as needed—and don’t let minor issues snowball into major problems.

[McSamuel]

When I first bought the car, I also encountered the issue of engine shaking. At red lights, the whole car body would tremble, even the accelerator pedal vibrated. The mechanic checked it and found a leaking ignition coil in the third cylinder, causing misfiring. After replacing the coil and spark plugs, it ran smoothly immediately. Worn engine mount bushings are also a major cause—when the rubber cracks, engine vibrations transfer directly into the cabin. Another time, I mistakenly filled up with 92-octane gasoline; the poor fuel quality caused unstable combustion, shaking like Parkinson's. Cleaning the throttle body and fuel injectors also helps, especially for cars that mostly drive at low speeds in the city, where carbon buildup can clog things up. I recommend getting a combustion analysis—the data won't lie.

[ValeriaRose]

Engine shaking issues should be investigated from three aspects: ignition, fuel supply, and mounting. Ignition system problems are the most common - spark plug erosion with excessive gap, ignition coil leakage, or aging cylinder wires can all cause misfire-induced shaking. On the fuel system side, clogged fuel injectors lead to uneven fuel distribution, while insufficient fuel pump pressure results in overly lean air-fuel mixture. Additionally, aging engine mounts are often overlooked - when those three rubber cushions crack, they completely fail to contain engine vibrations. It's recommended to first use a diagnostic tool to check for misfire codes, then measure cylinder pressure to rule out mechanical issues. A simple method is to unplug each ignition coil one by one at idle - if the shaking doesn't worsen, it means that cylinder wasn't working properly to begin with. For repairs, start by replacing spark plugs, then consider fuel system cleaning or replacing engine mounts.