What causes the idle speed not to return to normal when coasting in neutral gear in a manual transmission Lavida?

[DiHarper]

Manual transmission Lavida's idle speed not returning to normal when coasting in neutral gear can be attributed to the following reasons: Intake manifold leakage: When unauthorized air, fuel vapor, or combustion exhaust enters the intake manifold, it causes the air-fuel mixture to become too rich or too lean, leading to unstable engine idle. Excessive carbon buildup in throttle body: When carbon deposits accumulate excessively in the throttle body and surrounding intake passages, the cross-sectional area of the air passage changes. This prevents the control unit from precisely regulating idle air intake, also resulting in an overly rich or lean mixture and unstable idle speed. Intake system actuator malfunction: The engine intake system has numerous actuators, such as the throttle motor, idle speed control motor, duty cycle solenoid valve, air flow meter, and intake pressure sensor. Failure or damage to these components can cause unstable engine idle. Fuel system malfunction: Issues like clogged fuel injectors, blocked fuel filters, obstructed fuel pump screens, faulty fuel pressure regulators, or blocked return fuel lines can all lead to incorrect fuel injection quantities. This results in an overly rich or lean mixture and unstable idle speed. Ignition system malfunction: Problems such as faulty ignition modules, incorrect spark plug gaps, eroded or damaged spark plug electrodes, or excessive resistance in high-voltage wires can cause reduced ignition spark energy or misfires, resulting in erratic idle speed fluctuations.