What are the causes of low idle speed?

[AngelinaFitz]

The causes of low idle speed are as follows: 1. It may be due to inaccurate speed display caused by an inaccurate tachometer sensor. The idle speed is regulated by the computer and generally does not change without reason. 2. A dirty throttle body or a dirty mass air flow sensor can cause inaccurate intake data, leading to low idle speed. The solutions for low idle speed are as follows: 1. Check all intake system pipe connections and hoses for leaks, and whether the air filter is excessively dirty or clogged. 2. Inspect the idle air control valve. If the bypass passage inside the idle air control valve is clogged due to excessive carbon buildup, the intake air volume decreases, and the engine speed drops. For electronic throttle bodies without an idle air control valve, carbon buildup in the throttle body area may reduce idle air intake, causing low idle speed. 3. Check the exhaust gas recirculation (EGR) system. If the EGR valve is open during idle or if there is a hose leak, exhaust gas will enter the intake manifold, potentially reducing the proportion of fresh air in the air-fuel mixture and lowering idle speed. 4. Inspect the fuel evaporation system for leaks. If there is a leak in the hose between the fuel evaporation system and the intake manifold, more fuel will participate in combustion, but the intake air volume does not increase, resulting in an overly rich mixture, reduced combustion efficiency, and unstable idle. 5. Check if the fuel pressure is too low. If the fuel pressure is insufficient, fuel supply will be inadequate, leading to low idle speed. 6. Verify if the fuel injectors are functioning properly. Fuel injectors may become clogged due to excessive dirt, reducing fuel injection volume and causing low idle speed. 7. Check the connection circuit between the fuel injectors and the computer. If there is an open circuit or poor connection in one injector's wiring, causing the injector to fail to spray fuel or spray improperly, idle speed will drop. 8. Inspect the fuel for contamination. If the fuel quality is poor or contaminated, it will affect combustion efficiency, reduce combustion energy, and result in low idle speed. 9. Check the spark plugs for dirt, cracks, or wear. Verify if the spark plug gap is incorrect, if the electrodes are burned or damaged, and if the spark plug heat range is correct. 10. Inspect the spark plug wires for leakage, cross-firing, incorrect routing, and whether the resistance values are within the standard range. 11. Check the ignition coils for cracks, carbon buildup, and whether the primary and secondary coil resistance values are within the standard range. 12. Verify the signal wiring connection between the engine control module and the ignition control module, and ensure the power supply is normal. 13. Check the coolant temperature sensor and intake air temperature sensor. 14. Inspect the cylinder compression. If there is insufficient cylinder pressure or excessive variation between cylinders, engine performance will decline, idle speed will drop, and operation will become unstable.

[AsherLee]

I remember one time when my car's idle speed was too low, the engine RPM was below 700, while it should normally be between 800 and 1000. This caused the car to shake violently at startup and almost stall at a red light. After inspection, I found there were quite a few possible reasons: first, the throttle body was too dirty, with carbon buildup blocking the airflow; second, the air filter was clogged for too long, and replacing it made things much smoother; third, it could be due to dirty fuel injectors or insufficient fuel pump pressure; fourth, the idle air control valve might have had an issue, either stuck or with poor electrical contact. A leaking vacuum hose could also cause the idle speed to drop too low. Regular maintenance, including periodic cleaning of the intake and fuel systems, can help avoid such troubles.