What causes excessive fuel richness in cylinder bank 1 of Volkswagen CC at idle?

[VanMia]

Excessive fuel mixture richness requires checking for air leaks in the intake system. If none are found, the issue likely lies with the fuel injectors. A fuel injector atomization test or cleaning may resolve the problem. Introduction to car idle: Car idle is not a speed but rather an operational condition. When the engine runs without load, it's called idling. Releasing the accelerator pedal completely puts the engine in idle state. The rotational speed during idling is called idle speed, which can be adjusted by modifying throttle opening size. Generally, the optimal idle speed is the lowest RPM at which the engine doesn't vibrate. Function of car idle: Idling overcomes the engine's internal resistance, maintaining minimum rotation speed to facilitate driving and temporary parking. For example, during traffic light stops or congestion, though brief, temporarily shutting off the engine can achieve immediate energy-saving and emission-reduction effects.