What Causes Severe Idle Vibration in a New Car?

[JuliaLynn]

Here are the reasons for severe idle vibration in a new car: 1. Severe engine carbon buildup: When there is excessive carbon buildup inside the engine, it can cause idle vibration after a cold start. This happens because the excessive carbon deposits absorb the injected gasoline, resulting in an overly lean air-fuel mixture that makes starting difficult. The engine can only start once the mixture reaches a certain level, but then the excessive carbon buildup causes the mixture in the cylinders to become too rich, leading to engine vibration. 2. Ignition system issues: Problems with the ignition system can also cause idle vibration, typically due to excessive spark plug carbon buildup.

[Billy]

I also encountered this issue with my newly purchased car, and it was quite annoying. Severe idle shaking in a new car usually has several common causes: the engine mounts may not have been installed properly or the protective devices during transportation were not removed; there might be an issue with the fuel system, such as using the wrong fuel grade or unstable fuel pump supply; another possibility is an ignition system fault, like loose spark plugs or leaking ignition coils; the throttle body in new cars is very sensitive, and even slight dirt can easily affect the air intake; lastly, the engine control program may need an upgrade. I recommend going to the 4S shop for a comprehensive inspection immediately. They can use a computer to read the fault codes and pinpoint the issue—don’t try to fix it yourself, as the car is still under warranty.

[StReagan]

I remember my neighbor's newly bought car was shaking just as badly, and you could clearly feel it sitting inside. This kind of situation is most likely caused by an unbalanced engine operation. For new cars, the common reasons are mainly air trapped in the fuel system that hasn't been completely purged, or unstable fuel injector pressure. Additionally, the rubber components of the engine mounting brackets are particularly critical. New cars are often transported with screws securing them, which might not have been fully loosened. Another possibility is a stuck exhaust gas recirculation valve; even a slight issue with this component can cause unstable idling. If it's accompanied by black smoke from the exhaust pipe, it's most likely due to an overly rich air-fuel mixture. When checking, it's best to use an OBD scanner as well, focusing on the fuel trim values and throttle position sensor data.

[EvanAnn]

New car shaking is indeed frustrating. My colleague's car started shaking just one week after purchase. Later, it was found to be caused by a misfire due to poor contact in the ignition coil, with one of the four cylinders not working. Another easily overlooked issue is poor fuel quality in the tank; too much water content can lead to incomplete combustion. If the turbocharger's bypass valve in a new car gets stuck, it can cause significant fluctuations in intake pressure. Some high-end cars might have faults in their active engine mount systems, which are designed to absorb engine vibrations. It's advisable not to rush into dismantling the engine; first, check if the engine wiring harness is being squeezed or if there are loose connectors, as problems in these areas can be the most troublesome.

[LeGabriela]

When I first bought my car, it also had severe shaking, especially when the air conditioning was on. Later, the mechanic told me to mainly check three things: whether there was any vacuum leak in the intake system—even a small crack could let in air and affect the air-fuel mixture; the engine oil level must be precise—adding just half a liter extra in a new car can easily cause abnormal crankcase pressure; and also check the gap of the crankshaft position sensor, as improper installation can affect ignition signals. Additionally, if you've modified the center console or installed additional equipment, it might interfere with CAN bus signal transmission. New cars are particularly prone to carbon buildup from long-term low-speed driving—though the chance is small, it can't be completely ruled out. It's best to check the throttle opening angle in a cold state for more accurate results.