Rough idling in a 2018 Honda Accord can be caused by several issues ranging from simple maintenance problems to more complex mechanical failures. Here are some potential causes and solutions:

 
Dirty or Faulty Spark Plugs
 

• Faulty spark plugs can lead to incomplete combustion, causing the engine to idle roughly.
• Solution: Inspect and replace the spark plugs if necessary. It is recommended to check the spark plug gap and ensure they meet the manufacturer’s specifications.

 
Clogged Air Filter
 

• A clogged air filter restricts the airflow into the engine, resulting in an improper air-fuel mixture which can cause rough idling.
• Solution: Regularly check and replace the air filter. An air filter should typically be replaced every 15,000 to 30,000 miles, depending on driving conditions.

 
Fuel System Issues
 

• Clogged fuel injectors or a malfunctioning fuel pump can lead to inadequate fuel delivery, affecting engine idle smoothness.
• Solution: Use a fuel injector cleaner to clear any blockages or consider having the fuel injectors professionally serviced. Additionally, inspect the fuel pump and related components for faults.

 
Vacuum Leaks
 

• Vacuum leaks in the intake manifold or vacuum hoses can cause an imbalance in the air-fuel mixture, leading to rough idling.
• Solution: Inspect all hoses and connections for cracks or disconnections and fix any leaks.

 
Malfunctioning Idle Air Control Valve (IAC)
 

• The IAC valve controls the amount of air that enters the engine when the throttle is closed. A faulty IAC valve can lead to irregular idle speeds.
• Solution: Clean the IAC valve to remove any carbon deposits or replace it if cleaning doesn’t resolve the issue.

 
Mass Air Flow Sensor (MAF) Issues
 

• The MAF sensor governs the amount of air entering the engine. Dirt or damage to this sensor can result in a rough idle.
• Solution: Clean the MAF sensor with an appropriate cleaner or replace it if necessary.

 
Engine Timing Problems
 

• Incorrect engine timing can cause the engine to run poorly at idle. This could be related to a timing belt or chain issue.
• Solution: For this complex issue, it’s recommended to have a professional mechanic inspect the vehicle’s timing components.

 
Exhaust System Restrictions
 

• A clogged or faulty catalytic converter can cause rough idling as it restricts exhaust flow, increasing backpressure on the engine.
• Solution: Inspect the exhaust system for blockages or damage and replace the catalytic converter if needed.

 
It’s important to address rough idling promptly as it can reduce fuel efficiency and lead to more serious engine issues. Regular maintenance and inspections can help prevent many of these problems and keep your Honda Accord idling smoothly.