What Causes Idle Shaking in Automatic Transmission Vehicles?
2 Answers
Automatic transmission vehicles may experience idle shaking due to the following reasons: 1. Dirty Air Filter: The air filter is designed to protect the engine and reduce wear, typically requiring replacement every 10,000 kilometers. If not replaced in time, insufficient air intake can cause low idle speed, leading to engine shaking. Simply replacing the filter can resolve this issue. 2. High-Voltage Wire Breakage: A break in the high-voltage wire's core can affect ignition and cause engine shaking. Use a multimeter to measure resistance and replace the wire with significantly higher resistance. 3. Spark Plug Lifespan: Spark plugs have a limited lifespan. After 30,000 to 40,000 kilometers, their ignition efficiency significantly decreases, which can affect ignition. This is a common issue that can be resolved by replacing all spark plugs.
I dealt with a similar situation just last week. When an automatic transmission idles, shaking like a massage chair, the most common cause is worn engine mounts—those act like shock absorbers, and when they fail, engine vibrations transmit directly into the cabin. A dirty throttle body can also cause shaking, especially if you frequently encounter stop-and-go city traffic. If the spark plugs are due for replacement, misfiring cylinders can make the car jerk intermittently. Once, a friend’s car had clogged fuel injectors, causing unstable RPMs and resulting in body tremors. Poor fuel quality can make the engine 'cough,' so try adding a fuel system cleaner. The worst-case scenario is hardened carbon deposits inside the engine, making it run like a tractor. I recommend first scanning for trouble codes—if you don’t want to diagnose, just replace the engine mounts, as this is a common issue. If it shakes badly at red lights, get it checked ASAP.
