What adjustment is made if an engine is running too rich at idle?

When an engine is running too rich at idle, it means there is an excess of fuel in the air-fuel mixture being delivered to the engine. This condition can lead to inefficiency and poor combustion, causing issues like rough idling, increased emissions, and potential engine damage over time.

Lowering the fuel flow is the appropriate adjustment in this scenario. By reducing the amount of fuel delivered to the engine, the air-fuel mixture can be balanced more effectively. This increase in the air proportion relative to the fuel will help achieve the optimal stoichiometric mixture for combustion, thereby improving engine performance and efficiency.

Other options pertain to adjustments that might affect the overall engine operation but may not directly address the rich condition. For example, increasing air supply might seem like a solution, but it does not specifically regulate the amount of fuel being delivered, which is the main concern in a rich mixture. Changing the fuel type could alter the combustion characteristics, but it wouldn't be a practical or immediate response to an already rich condition. Adjusting the throttle position affects the airflow entering the engine but. like increasing air supply, does not directly adjust the fuel flow to correct the rich mixture. Therefore, lowering fuel flow is the targeted approach for rectifying a rich condition