What Causes Engine Shaking at Idle but Smooths Out When Accelerating?
1 Answers
Engine shaking at idle that smooths out when accelerating is a symptom of unstable idle speed, which is one of the most common faults in the daily maintenance of electronically controlled engines. The reasons for idle shaking that disappears upon acceleration include excessive carbon buildup on valves and intake pipes, malfunctions in idle control sensors and related circuits, among others. Below are detailed explanations of the specific causes: 1. Excessive carbon buildup on valves and intake pipes: Carbon deposits can absorb a certain amount of fuel, leading the electronic control unit (ECU) to make incorrect judgments. For example, if the ECU commands the injection of 100 units of air-fuel mixture but only 90 units actually enter the cylinder (with 10 units absorbed by carbon deposits), even if the remaining 90 units burn completely, the required power output cannot be achieved, inevitably causing shaking. 2. Malfunctions in idle control sensors and related circuits: For instance, if the idle switch fails to close, the ECU may mistakenly assume the engine is under partial load, leading to incorrect air intake control. Issues such as delayed or stuck idle valves due to oil contamination or carbon buildup, or a throttle valve not closing properly, can prevent the ECU from accurately adjusting the engine's idle speed. Additionally, faults in the intake air temperature sensor, air flow sensor, coolant temperature sensor, or short circuits/open circuits in sensor circuits can all result in unstable engine idle. 3. Leaks in the intake pipe and various valves: Common issues include cracked intake manifolds or poor sealing of intake manifold gaskets. When there are leaks in the air supply system, the ECU receives inaccurate air intake signals, leading to misjudgments and unstable engine idle.
