What Causes Engine Vibration at Idle When Warm?

[OElisa]

The causes of engine vibration at idle when warm are as follows: 1. Leaks in the intake pipe and various valves: Common issues include cracked intake manifolds or poor intake manifold sealing. When there is an air supply system leak, the engine's electronic control unit (ECU) receives inaccurate intake air volume signals, leading to misjudgment and resulting in unstable engine idle. 2. Excessive carbon buildup on valves and intake pipes: This causes the ECU to make incorrect judgments, failing to achieve sufficient power and resulting in idle vibration. 3. Malfunctions in idle control sensors and related circuits: For example, if the idle switch fails to close, the ECU mistakenly assumes the engine is under partial load, leading to incorrect air intake control. The idle control valve may respond slowly or get stuck due to oil contamination or carbon buildup, or the throttle valve may not close properly, preventing the ECU from making accurate idle adjustments. Additionally, issues such as short circuits or open circuits in sensors like the intake air temperature sensor, air flow sensor, coolant temperature sensor, and their circuits can also cause unstable engine idle. 4. Ignition system: Generally, spark plugs are a key component that can cause unstable engine idle. If a spark plug fails to ignite, it directly affects cylinder combustion, causing uneven power output among cylinders and leading to unstable engine idle.