What Are the Reasons for Unstable Idling and Shaking in Cars?
4 Answers
Car unstable idling and shaking reasons are: 1. The spark plug is damaged, the gap between the spark plug electrodes is worn out, leading to insufficient spark plug ignition, resulting in incomplete combustion of the air-fuel mixture; 2. Poor quality gasoline causes poor atomization effect of the fuel injector, leading to incomplete combustion of the mixture in the cylinder; 3. The throttle is dirty, and the fuel injector has excessive carbon deposits; 4. The fuel pump's fuel supply pressure is abnormal, or the intake pressure sensor's values are incorrect and functioning poorly. The function of the engine is to convert thermal energy into mechanical energy by expanding gas after combustion in a sealed cylinder, pushing the piston to do work, thereby providing power to the vehicle. The maintenance methods for the engine are: 1. Clean the air filter; 2. Remove sludge from the throttle; 3. Clean carbon deposits from the fuel injector.
I've been driving for over a decade and have encountered several instances of unstable idling and shaking, feeling like the car is trembling. The most common causes are carbon buildup in the throttle body or clogged fuel injectors. Carbon deposits can make the engine breathe unevenly, similar to a person holding their breath. Additionally, aging spark plugs can easily lead to uneven ignition, and there might be minor leaks in the intake system, such as cracked hoses or a dirty air filter that hasn't been replaced in time. These small issues can accumulate and make your car shake noticeably when stopped at a red light. I recommend regularly cleaning the throttle body. If the shaking becomes severe, don't delay—take it to a professional repair shop immediately to avoid bigger problems that could affect driving safety. Also, excessive carbon buildup is often related to poor fuel quality, so choosing reputable gas stations can help prevent some of these issues.
As someone who frequently works on car repairs, I've seen many cases of idle vibration. The root cause lies in the engine's uneven operation, such as issues with the ignition system: worn spark plugs or leaking coils can cause a cylinder to misfire. Or problems with the fuel system: clogged injectors can lead to unstable fuel supply, and insufficient fuel pump pressure is also a common culprit. On the air intake side, a dirty throttle body or intake manifold leaks can disrupt the air-fuel mixture ratio. Some cars experience sensor failures, like oxygen sensors providing incorrect data, causing the ECU to lose control accuracy. For diagnosis, it's essential to use an OBD scanner to read fault codes—don't just guess. A simple check involves observing whether the idle RPM gauge fluctuates significantly or listening for intermittent engine sounds. Ultimately, it's best not to attempt DIY repairs; instead, have a professional technician conduct a thorough inspection. After all, vibration can indicate serious underlying issues—don't risk safety to save money.
As I've gotten older, I've driven quite a few cars, and idle shaking is most common in older vehicles. My old car had this issue too, mainly due to excessive carbon buildup—the throttle body and spark plugs were clogged with oil deposits, causing the car to rock back and forth when starting. It could also be loose belts or imbalanced pulleys on the alternator or AC compressor, which make the engine shake when running. Fuel system problems are another culprit: poor-quality gasoline or a clogged fuel filter can disrupt fuel delivery. I usually start by replacing the spark plugs myself—it's low-cost and easy to do. But for serious cases, I’d take it to a mechanic, as issues like electrical shorts or aged wiring are too complex to handle alone. Regular maintenance, especially cleaning the intake system, can reduce shaking and make driving much smoother.
