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Engine idle speed is the speed, measured in revolutions per minute (RPM) an engine is designed to run at when the engine is fully warmed up and the vehicle is stopped in park or neutral. Typically, the idle speed will be set at a value in the range of 600 to 800 RPM, but the exact value will depend on the number of engine cylinders and whether the vehicle is equipped with a manual or automatic transmission. Idle speed is maintained by the throttle body working in conjunction with the vehicle’s powertrain control module.
The repair procedure depends on the exact cause of the high idle. The below lists common causes of high idle and in each case, the appropriate vehicle system, components, and parts involved would be inspected, removed for repairs, and/or replaced as needed.
Faulty Fuse: In the majority of vehicles, engine idle speed is controlled via an idle control valve (ICV). A faulty or blown fuse in other electronically controlled systems can cause the Idle Air Control (IAC) motor to malfunction, leading to a higher than normal engine idle speed.
Faulty Idle Air Control Valve (ICV): Some cars are equipped with an idle air control valve to maintain idle speed. This part can malfunction due to excessive carbon buildup in the intake manifold.
Vacuum Leak: On any engine, a vacuum leak will cause a high engine idle as the oxygen sensor detects lean operation and the engine computer then tries to compensate, which can result in abnormal idle. Malfunctioning Throttle: A malfunctioning throttle system can cause both a high or low idle as well as an engine stall. A dirty air intake or cracked air intake tube is often the culprit. Computer Malfunction: If the powertrain control module is malfunctioning, idle speed may be affected.
No. High idle speed could make your vehicle difficult to control and were the idle speed to suddenly and unexpectedly increase to really high levels, you could experience unintended acceleration. Even moderately high idle speed, that is up to 1,200 RPM will make it more difficult to slow your vehicle when stopping and, once stopped, there remains the risk of your foot coming off the brake and the car jumping ahead. High idle speed also wastes gas and can be distracting as the vehicle does not perform as expected.