What causes unstable idle speed without fault codes in the 2012 LaCrosse?

[VanFelicity]

The reasons for unstable idle speed without fault codes in the 2012 LaCrosse are: 1. Intake manifold leakage: When unauthorized air, gasoline vapor, or combustion exhaust enters the intake manifold, it causes the air-fuel mixture to become too rich or too lean, leading to unstable idle speed. 2. Excessive carbon buildup on the throttle body: Carbon deposits on the throttle body and surrounding intake passages alter the cross-sectional area of the air passage, preventing the control unit from precisely regulating idle air intake. This also results in an overly rich or lean mixture, causing unstable idle speed. 3. Damaged intake system components: The engine's intake system has many components, such as the throttle motor, idle speed stepper motor, duty cycle solenoid valve, air flow meter, and intake pressure sensor. Faults or damage to these components can cause unstable idle speed. 4. Fuel system blockage: Issues like clogged fuel injectors, fuel filter, fuel pump screen, faulty fuel pressure regulator, or blocked return line can lead to incorrect fuel injection, causing the air-fuel mixture to become too rich or too lean and resulting in unstable idle speed.