What Causes Unstable Idling and Shaking in the Engine?

[McWillow]

The causes of unstable idling and shaking in the engine are: 1. Aging of rubber components inside the engine mounts and transmission mounts; 2. Improper air-fuel mixture ratio in the engine compartment; 3. Carbon buildup on the valves and intake ports inside the engine, which absorbs a portion of the sprayed fuel-air mixture, reducing engine power and causing vibrations; 4. Malfunction of the coolant temperature sensor; 5. Improper air-fuel mixture ratio in the engine compartment. An engine is a machine that converts other forms of energy into mechanical energy, including internal combustion engines, external combustion engines, jet engines, and electric motors.

[VanJourney]

My old car was shaking like an earthquake at idle last month, with the RPM fluctuating up and down, so I started troubleshooting it myself. The ignition system was likely the issue, such as excessive carbon buildup on the spark plugs or aging ignition coils. When I took them apart, sure enough, the spark plugs were all black with carbon deposits. After replacing them with new ones, it improved significantly. Clogged fuel injectors can also cause uneven fuel supply—I checked and cleaning agents didn’t help, so I might need to replace the parts. Additionally, a dirty throttle body can restrict airflow, but spraying it with cleaner improved the situation a bit. I’ve been learning DIY car repairs for a while, and this kind of shaking is common in older models. Using fuel additives regularly can prevent carbon buildup. Don’t ignore it—delaying repairs could lead to increased fuel consumption or even engine damage. I’ve saved quite a bit on repair costs by doing it myself.

[DelEvangeline]

I've driven for over a decade and encountered engine idle vibration multiple times, usually due to fuel system or sensor issues. When spark plugs reach the end of their lifespan with worn filaments, they cause uneven ignition leading to unstable idling. Fuel pump or injector clogs result in unstable fuel supply causing severe shaking - I personally experienced this and fixed it by replacing parts. Additionally, intake manifold leaks or throttle valve carbon buildup can disrupt air-fuel mixture balance. Faulty oxygen sensors may also interfere with control systems - I discovered mine malfunctioned during last inspection. For older vehicles, I recommend regular maintenance with quarterly checks on related components to avoid costly overhauls.

[VanEthan]

As a new car owner, I've been quite nervous because my engine keeps shaking at idle shortly after buying the car. Fellow car enthusiasts suggested it might be time to change the spark plugs or that the fuel injectors are clogged, with other possible causes being a dirty air filter affecting air intake. Not being very technical, I took it straight to the repair shop. The mechanic checked and said it was just a loose ignition coil, and tightening it fixed the issue. The advice for us beginners is not to panic but also not to delay to prevent the problem from worsening—safety first. Simply check the external wiring of the engine, and if there are any unusual noises, take it to a professional shop for inspection. It won't cost much.