The causes of high idle speed in a car include: stuck electronic throttle that fails to close tightly; faulty idle control valve; malfunctioning coolant temperature sensor; intake manifold air leaks; and faults in the power steering system pressure controller of the vehicle's air conditioning system. Faulty Idle Control Valve: In fuel-injected engines, normal idle speed is determined by the idle control valve. The electronic control module calculates signals from engine speed, temperature, throttle switch, and air conditioning, then adjusts the idle control valve to open the intake bypass channel or directly increase the throttle opening degree, thereby increasing the air intake to raise the engine idle speed. If oil residue or carbon deposits cause the idle control valve to stick or the throttle to fail to close properly, the electronic control unit cannot accurately adjust the engine idle speed. Intake Manifold Air Leaks: Under normal conditions, the air intake must be strictly controlled. If there is an air leak in the intake system, the air flow sensor cannot measure the true air intake, leading to inaccurate control of the air intake by the electronic control module and resulting in unstable idle speed. Fuel Injector Leakage or Blockage: If the fuel injector leaks or is blocked, it cannot follow the electronic control module's instructions for fuel injection, causing the air-fuel mixture to become too rich or too lean. This results in poor performance in certain cylinders and idle speed fluctuations.
