What Causes Low Idle Speed in a Car?

[Ella]

Low idle speed in a car may be caused by low battery voltage; carbon deposits; the control unit receiving incorrect signals and issuing wrong commands, leading to inaccurate control of engine idle air intake and abnormal combustion. It can also result from faulty idle air actuators causing inaccurate idle air control. The impact of idle speed on gasoline engines is as follows: 1. Fuel Economy: Since engines often operate at idle, statistics show that about 30% of urban vehicle fuel consumption occurs during idle. Therefore, reducing fuel consumption during idle is crucial, which is also a requirement for idle control. 2. Emissions: During idle, gasoline engines have a high amount of residual exhaust gas in the cylinders. To ensure stable combustion, the mixture needs to be enriched, leading to incomplete combustion and the production of harmful emissions like CO and HC. Experiments prove that lower idle speeds increase the dilution effect of exhaust gases, further raising CO and HC emissions. Thus, increasing idle speed helps reduce CO and HC emissions. Relevant data and experiments show that increasing engine idle speed from 700r/min to 800r/min reduces CO by 10% and HC emissions by 15%.