Why Honda Accord Check Engine Light Flashing Rough Idle?

One thing that you don’t want to see on your Honda Accord is a rough idle accompanied by the check engine lighting up. As intimidating as that can seem, it is an issue that can be managed if you know how to properly deal with it.

The check engine light turning on at rough idle indicates that you have a problem with one of the internal components such as a loose gas cap, faulty airflow sensor, faulty/damaged oxygen sensor, faulty catalytic converter, etc.

Once you identify the core problem, the problem becomes much more manageable. Below we go through some of the common causes of this problem and their respective solution.

Why does the Honda Accord check engine light flash at a rough idle?  

The following are some of the most common causes of the Honda Accord check engine light flashing at rough idle.

1. Gas Cap Loose

The gas cap plays a critical role in the Honda Accord vehicle. It ensures that no gas escapes when the engine is turned off and provides a seal on the fuel system to keep maintaining pressure on the fuel tank.

A torn or old seal on the gas cap would result in the loss of more gas thereby requiring more refilling from the fuel pump.

2. Faulty Airflow Sensor

Airflow sensors detect the amount of air going into the engines running on fuel. If the sensor becomes dirty, the engine may start stalling and idle rough.

By detecting the amount of airflow, it determines how much fuel is needed in the engine for it to operate with efficiency. Depending on factors such as altitude, it may readjust the amount of fuel being used.

3. Damaged Spark Plugs

Spark plugs are very critical to the Honda Accord as they are the devices that cause the air inside the engine to combust and as a result, move the piston that runs the engine.

If the spark plugs or the wires that carry the spark from the ignition coil are worn, the result is the vehicle will experience reduced power and driving performance.

If the damage is more severe, you will experience rough idling or stalling.

4. Faulty Or Damaged Oxygen Sensor

Oxygen sensors determine the amount of oxygen present in the Honda Accord vehicle after every combustion inside the engine.

When the oxygen sensor is faulty or damaged, there will be irregularity in the timing of combustions which may result in rough idling, stalling, and decreased acceleration.

5. Faulty Catalytic Converter

Catalytic converters on the Honda Accord are a key component of the exhaust system that converts harmful carbon monoxide from the combustion engine into relatively less harmful carbon dioxide.

When the catalytic converter is damaged, it causes the vehicle to idle roughly.

How to Fix the honda accord check engine light flashing rough idle? 

Luckily a benefit of the Honda Accord is that if the check engine light starts flashing and you see the vehicle rough idling, then there are various error codes to indicate what the problem is.

Each of the problems that we discussed in the previous section has a specific code associated with it.

Check the diagnostics manual for those error codes and then once you identify the problem, resolve the issue by following the processes that we are discussing below.

1. Loose Gas cap: Install a new gas cap

Other than the check engine light flashing, you may also notice a smell of fuel coming from the vehicle. Another symptom is that the cap will not tighten easily.

You can solve this issue by installing a new gas cap by following these steps.

  • Step 1: Prepare the vehicle

Start by parking the vehicle on a level surface and keeping it locked with chocks. Make sure the transmission is in park mode.

  • Step 2: Take off the gas cap

Unlock the fuel door for access. Then unlatch the gas cap and take off the fuel door cable.

You might find a gasket at the bottom of the gas cap. Inspect for any cracks. If you find any cracks, then it indicates that the gas filler neck is faulty and needs replacement.

  • Step 3: Clean the gas filler neck threads

Take a dry but clean cloth or tissue paper to clean up the threads on the gas filler neck.

  • Step 4: Install a new gas cap

Use a screwdriver to latch the new cap onto the gas filler neck. Check that the threads are fully locked tight.

  • Step 5: Reattach the cable to the fuel door

To check for leaks or escaping gas, use a gas detector. Make sure that the fuel container is fault-free before you lock the fuel door shut.

  • Step 6: Check for warning lights

Check whether the warning lights appear on the dashboard. If not, then you are good to go.

2. Faulty Airflow Sensor: Replace the Airflow Sensor

You will notice that the engine shows signs of stalling, difficulty turning over, engine hiccups, etc. when there is a faulty airflow sensor.

To fix this issue, replace the faulty airflow. The following steps show how to change it.

  • Step 1: Disconnect the electrical connections

Start by disconnecting the negative terminal and then disconnecting the air flow sensor from the electrical connector.

  • Step 2: Gain access to the mass airflow sensor

Take a screwdriver to remove the air intake hose clamp. Take out the air intake tube after taking off the clips attaching the air filter housing.

You may also take the opportunity to remove the air filter. Use a flathead screwdriver to unfasten the air intake hose clamp at the throttle body.

Remove the clips securing the air filter housing and lift out the air intake tube. This is a good time to replace the air filter.

  • Step 3:  Remove the mass airflow sensor

Use a socket and ratchet to unbolt the MAF sensor from the air intake tube. Then carefully slide the sensor out of its housing.

  • Step 4: Install the new mass airflow sensor

Take the new sensor and slowly but carefully slide it into the air intake tube. Be sure to not touch the temperature sensor wire as that can cause the temperature sensor to produce inaccurate readings.

  • Step 5: Complete the installation

Rotate the sensor to around 7-12 kg. Then place the air intake tube back in. Recouple the electrical wire to the sensor and then use a screwdriver to make the hose clamp tighter.

Recouple the negative terminal too.

3. Damaged spark plugs: Replace Spark plugs

When the spark plugs are damaged, you will notice engine misfires, reduced acceleration as well as excessive fuel usage. There is no fixing a damaged spark plug, so it is best to simply replace it.

  • Step 1: Access The Spark Plugs

Raise the hood and look for spark plugs. You will find them underneath the engine covers that you must remove. Be careful about the slotted fasteners holding the covers so that you don’t break them.

Unbolt the ignition coils and then detach the coils from the wiring harness. Remove the coils from the plugs and leave them aside for the upcoming steps.

  • Step 2: Removing The Spark Plugs From The Engine

As you can access the spark plugs now, now you can start unplugging them. It is the same for every single plug. To remove the plugs, you will need to use a socket to detach them from the engine block.

The sockets will have an insert that will grasp the plugs. For bare sockets, you can roll up a piece of paper and insert that into the plugs.

  • Step 3: Gap The New Plugs

Use the plug gapping tool to determine the gap between the spark plugs.

  • Step 4: Re-Install Spark Plugs Into The Engine

Install the plugs by inserting them into the spark plug socket. To keep the threads protected, you have to start with finger tightening. Make sure to tighten it according to the specified torque measurements and not more.

Excess tightening may result in damage to the plug or the engine.

  • Step 5: Replace The Wires And Covers

Take off the coil on the spark plugs and replace them. Then gently but firmly push the plugs down until they are properly placed. Use the bolts to make them tight and then attach them with the electrical connections.

4. Faulty oxygen sensor: Replacing the oxygen sensor

When the oxygen sensor becomes faulty, you will notice a smell similar to that of a “rotten egg”. You will also find black exhaust smoke associated with reduced fuel efficiency.

  • Step 1: Set up the Honda Accord for the process

Using a jack, lift the Honda Accord. Use the leverage of the front jack point to raise the Accord. Then place the jack stands underneath the front portion and slowly lower the Accord to place it on the stands.

  • Step 2: Remove the O2 sensor

Carefully remove the oxygen sensor leads from the factory cable harness. Then slowly rotate the oxygen sensor anti-clockwise to remove it. You will need a socket wrench as well as an oxygen sensor socket.

  • Step 3: Install the new oxygen sensor

Place the new oxygen sensor where the old one was previously. Do the previous steps in the opposite order for the assembling of the sensor.

5. Faulty catalytic converter Replace catalytic converter

Catalytic converters usually last very long, but over time, they can become prone to contamination, clogging, and the effects of overheating.

Their symptoms are similar to other causes of rough idle such as reduced acceleration, engine light flashing, reduced fuel efficiency, etc.

The following steps show how to properly replace the catalytic converter on the Honda Accord.

  • Step 1: Lift And Secure The Vehicle

Set the vehicle to a parking brake and then use chocks to keep the wheels from moving. Then use a jack to raise the vehicle.

  • Step 2: Remove Bolts On The Front And Rear Flanges

The catalytic converter is screwed in line with the remaining components of the exhaust system with 5 bolts. To remove these bolts, you can use a ratchet and a wrench. After unbolting it, you can remove the catalytic converter.

  • Step 3: Clean The Surface Area Of The Mounting Points

Often you will notice a significant buildup of debris and rust on the mounting surfaces at the back and front. You can use a wire brush to clean it up. Doing this helps the surface become ready to receive new seals.

It also helps to get a firm fit.

  • Step 4: Install New Catalytic Converter Seals

After cleaning the rust and debris, you can now put in new seals on the catalytic converter.

  • Step 5: Install New Bolts And Springs

Now you can put in the mounting bolts on the front and rear flanges. Once the bolts are tightly screwed, you can free the vehicle from the jack stands and lower it down.

Frequently Asked Questions [FAQs]

Since there are several different possible answers for why the check engine light is flashing at rough idle, users will have a lot of questions regarding that. Below we look at some of these commonly asked questions.

What Does It Mean When Your Honda Accord’s Check Engine Light Flashes?

The check engine light flashing indicates an engine misfire or a disruption within the fuel combustion system. When it flashes at rough idle, it indicates problems with one of the gas caps, catalytic converter, oxygen sensor, mass airflow sensor, etc.

How Much Does It Cost To Fix A Honda Accord Check Engine Light?

Some of the problems that result in the check engine light flashing can be resolved with a simple DIY fix that costs less than $80-90.

But when it comes to more sophisticated problems such as a catalytic converter, costs can exceed over $1000.

How Can I Tell If My Honda Accord Check Engine Light Sensor Is Bad?

Check the battery, alternator, and the rest of the electrical connections to confirm whether the check engine light sensor is functioning properly.

If there are no problems with the connections, then use the diagnostic codes to identify the issue.

Can I Drive My Honda Accord With The Check Engine Light Blinking?

You would be better advised to not drive the vehicle when the check engine light comes on. Diagnose the problem before trying to drive the vehicle.


Whenever the check engine light starts flashing on the Honda Accord combined with a rough idle, make sure to check what the problem is first since the causes are numerous. Following the diagnostic codes will help.

One important thing to remember is to make sure to dispose of the excess fluid in an environmentally safe manner when replacing the gas cap.

Also, make sure to take all forms of safety precautions when working on the electrical connections. And make sure that the replaced parts are the exact size and specifications of the old ones.

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