Why does the car shake severely when starting?

[StRowan]

The reasons for severe shaking when starting the car: 1. Engine mount issue: If the car shakes while idling in place, the engine mount needs to be replaced; 2. Carbon deposit problem: Excessive carbon deposits on the pistons or spark plugs can cause the fuel injected by the fuel injector to be absorbed by the carbon deposits during cold starts, preventing it from participating in combustion. This leads to incorrect air-fuel mixture, unstable idling, shaking, or even misfiring; 3. Incorrect air-fuel mixture ratio: This involves multiple factors, such as the atomization condition of the fuel injector, the ignition condition of the spark plugs, the data from the intake pressure sensor, the air intake data from the mass air flow sensor, the fuel pump pressure issue during cold starts, and the environmental temperature data from the ECU, all of which need to be checked.

[NoahLee]

I had the same issue last time I started my car—the engine was shaking like a massage chair. This is a pretty common problem, mostly caused by excessive carbon buildup clogging the fuel injectors, leading to poor combustion. Worn-out spark plugs are also a major culprit, especially if they haven’t been replaced after 50,000–60,000 kilometers—they can even leak electricity during ignition. Don’t overlook aging engine mounts either; if they’re cracked, the vibration damping is toast. Poor-quality fuel or overdue oil changes could also be to blame, as insufficient lubrication increases friction. If the idle speed fluctuates wildly with strange noises, get the trouble codes scanned ASAP—it’s likely a faulty ignition coil or oxygen sensor. Don’t try DIY fixes blindly. Last month, my neighbor stripped the spark plug threads while removing them himself and ended up paying an extra 800 bucks to repair the cylinder head.

[Maxine]

I've researched this issue multiple times. The shaking is more noticeable during cold starts, right? It's most likely due to the disruption of the engine's three balances. Either there's a misfiring cylinder, and the ignition coils and spark plugs need replacement, or there's an issue with the fuel system—either a clogged fuel filter or excessive carbon buildup in the fuel injectors. A vacuum leak can also cause shaking; a cracked rubber hose can draw in excess air. Additionally, worn engine mounts, especially in front-wheel-drive cars, can transmit vibrations directly into the cabin if the rubber mounts are cracked. A dirty throttle body can also disrupt airflow, leading to an imbalanced air-fuel mixture. I recommend opening the hood during a cold start and feeling the engine with your hand. If it wobbles significantly from side to side, the engine mounts are likely the culprit. Don't delay fixing it—prolonged carbon buildup becomes harder to clean.

[MadelineAnn]

I just dealt with this issue last weekend. The car shook like crazy upon starting. The mechanic ran a computer scan and found a misfire in cylinder three. Replacing the spark plugs fixed it immediately. Actually, there are just a few common causes for engine shaking: ignition system failures are the most frequent, like leaking ignition coils or worn spark plug electrodes; fuel system issues such as clogged injectors or insufficient fuel pump pressure; broken engine mount cushions are also very common; and excessive carbon buildup causing uneven combustion chamber pressure. Focus on checking four areas: listen to the engine sound at startup to identify any cylinder misfires; turn on the AC to see if the shaking worsens—if so, the engine mounts are likely the culprit; if the RPM is unstable when revving in neutral, it's probably carbon buildup. For a simple fix, try changing the spark plugs first.

[Lena]

This scenario is all too familiar, commonly seen in older vehicles over five years. It mainly falls into two categories: mechanical and electrical. On the mechanical side, check the engine mount bushings—if the rubber has aged, it loses its damping effect. For the electrical part, focus on the ignition system; excessive spark plug gap or cracked ignition coils can cause misfires. Also, don’t overlook fuel pressure—a clogged low-pressure fuel pump filter can lead to insufficient fuel supply. Last time my car shook, it was due to a leaking intake pipe caused by a cracked $3 sealing ring. I recommend observing the exhaust pipe; if it’s puffing black smoke with a gasoline smell, incomplete combustion is certain. Start by replacing the spark plugs and air filter—most issues can be resolved for around a hundred bucks. If the shaking persists, you’ll need an OBD scanner to read the data stream.