What Causes Unstable and Fluctuating Car Idling?
2 Answers
Car idling becomes unstable and fluctuating due to the following reasons: 1. Improper air-fuel mixture ratio in the engine compartment; 2. Prolonged use of spark plugs leads to aging of the ignition coil, high-voltage wire deterioration, and leakage issues, resulting in reduced ignition capability; 3. Carbon buildup on the engine valves and intake passages, which absorbs a significant portion of the injected fuel-air mixture, thereby decreasing engine power; 4. Malfunctioning coolant temperature sensor. Solutions for unstable car idling include: 1. Replacing spark plugs; 2. Cleaning valves and intake passages; 3. Inspecting the coolant temperature sensor.
Unstable idle speed with fluctuating RPM is quite a headache. From my experience, the main causes are issues in the intake system: excessive carbon buildup in the throttle body blocking airflow, or a sluggish idle control valve stuck by dirt; or an intake pipe leak causing vacuum loss, affecting stability. Fuel problems like clogged injectors leading to uneven fuel supply, and unstable ignition from old spark plugs are also common culprits. Additionally, faulty sensors like a damaged oxygen sensor can confuse the ECU. Small issues accumulating make the car seem like it's gasping, and prolonged neglect can increase fuel consumption or even damage the catalytic converter. Cleaning the intake and throttle body every six months helps a lot; for severe carbon buildup, DIY or professional cleaning is needed. Don’t delay when noticing abnormalities—prompt checks prevent major repairs and keep the engine running healthily.
