Which of the following is a common symptom of a stuck-closed EGR valve?

A stuck-closed EGR (Exhaust Gas Recirculation) valve is often associated with increased NOx (nitrogen oxides) emissions. The EGR valve serves to recirculate a portion of the exhaust gases back into the intake system. This process lowers the combustion temperature, which helps to reduce the formation of NOx emissions.

When the EGR valve is stuck closed, exhaust gases are unable to mix with the incoming fresh air-fuel mixture. As a result, the temperature in the combustion chamber remains high, leading to an increase in NOx production. Under normal circumstances, the EGR valve helps to mitigate this by allowing some exhaust back into the intake, hence controlling combustion temperatures effectively. Therefore, high NOx emissions are a direct symptom of a malfunctioning EGR system when the valve is stuck in the closed position.

The other symptoms, while they can be related to various engine issues, are not directly caused by a stuck-closed EGR valve. Understanding the role of the EGR system is crucial for diagnosing emissions-related problems effectively.