Why does the car occasionally shake at idle speed?
4 Answers
Car occasionally shaking at idle speed is mainly caused by the following reasons: engine carbon deposits, aging or carbon deposits on spark plugs, dirty engine throttle, and poor fuel flow. Here are more details on the solutions: 1. Clean carbon deposits from spark plugs or replace them with higher-quality, more expensive spark plugs. 2. If the center electrode of the car's spark plug is made of nickel alloy, it is recommended to replace it every 20,000 to 30,000 kilometers. If both the center and side electrodes of the car's spark plug are platinum or iridium, it is recommended to replace them every 80,000 kilometers, and clean the carbon deposits from the spark plugs when necessary. If only the center electrode of your car's spark plug is platinum or iridium, it is recommended to replace it every 40,000 to 60,000 kilometers.
My car used to idle as shaky as a massage chair, and later I found out it was due to thick carbon buildup on the throttle. That layer of black sludge blocked half of the intake, causing the engine to sputter and shake like it was having a seizure. Spark plugs are also crucial—if the electrodes are worn or the gap is incorrect, it can lead to misfiring. I've also encountered older cars with worn-out engine mounts, where the rubber cracked like a turtle shell and completely lost its damping effect. This is no small matter. I recommend cleaning the throttle every 20,000 kilometers and replacing the spark plugs every 50,000 kilometers. Unstable idling is most annoying when it happens at a red light, making your whole body tremble along with the car. Fixing it early is the way to go.
Just helped a friend deal with idle vibration issues last week, and it turned out to be caused by poor fuel quality. Long-term use of cheap fuel led to gum deposits clogging the fuel injectors, making the fuel supply unstable like a blood clot in the fuel line. Spark plug erosion is also common, especially with aged plugs where the electrode gap exceeds 1mm, cutting ignition energy by half. We also checked cylinder compression and found that uneven pressure across the four cylinders can cause resonance. Remember to inspect the engine vacuum hoses for cracks, as leaks can lead to an overly lean air-fuel mixture. Regular maintenance should include checking the air filter, as a clogged one can suffocate the engine. Don’t delay addressing issues; severe carbon buildup can score the cylinder walls.
My car repair notes say: Idle shaking is 80% likely due to aging ignition coils. Last time, that Touareg was shaking so badly the tea cup was dancing, and after testing, it was found that the three-cylinder coil's output voltage was unstable. Clogged fuel injectors are also common, especially with long-term short-distance driving, where impurities in the gasoline deposit in the injectors. Another often overlooked issue is a faulty exhaust valve; a leak here can cause abnormal crankcase pressure. It's recommended to first read the fault codes, focusing on whether the oxygen sensor data stream is abnormal. You can check the engine mounts yourself by using a flashlight to see if the rubber has any signs of cracking. Fixing it isn't hard; replacing parts can solve 90% of the shaking problems.
