The FAA has issued an airworthiness directive affecting Cessna 172s built since 1996. These aircraft can develop an overly rich idle mixture that can stop the engine from operating when the pilot reduces power to idle for a landing approach, power-off stalls, etc. The pilot might not be able to get the engine restarted. The AD advises pilots to lean the mixture slightly if the engine won't restart.
The AD requires an inspection to ensure a proper idle mixture setting. This inspection doesn't require a mechanic and can be accomplished by a properly licensed pilot. (AOPA has been a longtime advocate of such simplified inspections.) New information on idle power engine roughness must also be added to the pilot's operating handbook.