What Are the Reasons for Low Idle Speed During Cold Start?
2 Answers
Reasons for low idle speed during cold start include: carbon buildup in the throttle body, dirty intake passages, and weak spark due to faulty spark plugs, which should be cleaned or replaced promptly. Below are detailed explanations of the related causes: 1. Prolonged vehicle usage can lead to clogged intake passages, carbon deposits or oil accumulation in the throttle body, resulting in unstable or low idle speed. Carbon buildup in the throttle body affects air intake, causing low idle speed during cold starts. It is recommended to clean the throttle body and intake passages to prevent abnormal idle conditions. 2. Over time, spark plugs can also accumulate carbon deposits. Severe carbon buildup may cause weak sparks in some cylinders, affecting vehicle performance and leading to low idle speed. Timely cleaning or replacement of spark plugs is advised. 3. A clogged fuel injector can cause insufficient fuel pressure and poor fuel atomization, leading to unstable or low idle speed. If the vehicle's intake pipe malfunctions, the air-fuel mixture ratio may become imbalanced, potentially causing excessive emissions and failure to pass annual vehicle inspections.
The other day when I started my car in the dead of winter, the idle speed was unusually low, with the tachometer dropping to around 600 RPM. It felt like the car was struggling to breathe. This is usually because during a cold start, the engine requires more air and fuel to warm up quickly. However, if there's an issue with the coolant temperature sensor signal—for example, if it incorrectly reads that the engine is already warm—it won't increase the idle speed. Alternatively, if the mass airflow sensor isn't reading accurately, leading to insufficient air intake, the RPM will remain low. Prolonged conditions like this can easily cause stalling or wear out components. I recommend that if you frequently encounter this situation, you should first check whether the sensors and the electronic control unit are functioning properly. Don’t wait until the problem worsens to address it. Additionally, try to park in a garage during winter to avoid extreme cold.
