What Causes Engine Idle Vibration in a New Car?
2 Answers
Reasons for engine idle vibration in a new car include: severe engine carbon buildup, issues with the ignition system, unstable oil pressure, aging engine components, dirty throttle body, excessive carbon buildup in the fuel injectors, etc. When there is significant carbon buildup inside the engine, the gasoline sprayed by the cold-start injector is largely absorbed by the carbon deposits, resulting in an overly lean air-fuel mixture during cold starts and making it difficult to start. In this situation, the engine only starts easily once the carbon deposits have absorbed enough gasoline to become saturated. After starting, the gasoline adsorbed on the carbon deposits is then drawn into the combustion chamber by the engine's vacuum suction, enriching the air-fuel mixture. This fluctuation between lean and rich mixtures causes idle vibration after a cold start.
When I first bought my car, it had idle vibration issues, which were likely caused by rapid carbon buildup during the break-in period or the use of low-quality fuel. The engine was too new, and the cylinder walls hadn't smoothed out yet, causing incomplete combustion and severe shaking due to carbon deposits. If the spark plugs were improperly installed or mismatched, they could also lead to misfires and unstable idling. Issues in the intake system, such as a throttle body clogged with oil residue or minor leaks, could create an imbalance in air intake and exhaust, making the engine shake noticeably. My advice is not to rush into repairs. First, try using higher-grade fuel from reputable gas stations and drive a few hundred kilometers to see if the issue improves. If the vibration persists, take it to a 4S dealership for a free inspection of assembly quality or throttle body cleaning—this is crucial during the new car warranty period.
