What is an indication of a defective fuel injector?

A rough engine idle or misfiring is a classic indication of a defective fuel injector. This occurs because a malfunctioning injector may not deliver the correct amount of fuel to the engine cylinders, leading to an imbalance in the air-fuel mixture. When the air-fuel mixture is not optimal, it can cause the engine to run unevenly, resulting in a rough idle or misfires during operation. Misfiring happens when one or more cylinders do not ignite properly, further contributing to engine performance issues, vibrations, and potentially leading to greater engine damage over time.

The other options reflect positive or normal operation characteristics of an engine. Improved engine response and smoother engine operation indicate that everything is functioning optimally, which would not be expected with a defective fuel injector. Decreased oil consumption is not typically related to injector performance; rather, it may suggest an engine that is running efficiently or has been maintained well, without indicating any issues with the fuel delivery system.