A rough idle should never be ignored. It can reduce fuel economy, damage components over time, and eventually leave you stranded. In this guide, we’ll explain the top reasons an engine runs rough at idle, how to diagnose the problem, and when replacing the motor with a used engine or choosing quality used engines may be the smartest solution. https://carengineguru.com/engine-running-rough-at-idle-top-causes-smart-fixes-for-2026/