What can improper spark plug operation lead to in terms of emissions?

Improper spark plug operation can significantly affect vehicle emissions, primarily leading to higher exhaust emissions. When spark plugs are not functioning correctly, they can cause incomplete combustion of the air-fuel mixture in the engine. This incomplete combustion results in unburned fuel being expelled into the exhaust system, which contributes to pollutants such as hydrocarbons and carbon monoxide being released into the atmosphere.

Additionally, if the spark plugs are misfiring or firing inconsistently, it can lead to an increase in nitrogen oxides (NOx) as the combustion process becomes erratic. Overall, the efficiency with which the engine burns fuel is compromised, leading to an increase in harmful emissions.

In contrast, increased fuel efficiency, improved throttle response, and reduced engine noise are not outcomes associated with improper spark plug operation. Instead, these elements would typically signify an engine functioning optimally with well-operating spark plugs. Therefore, the correct understanding focuses on how improper spark plug performance directly contributes to elevated levels of exhaust emissions, highlighting the importance of maintaining and replacing spark plugs as necessary for emission control and overall engine health.