No Check Engine Light But Car Runs Rough: 5 Causes and Fixes Light?

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no check engine light but car runs rough

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The check engine light in your car highlights the result of a malfunction such as engine overheating or low oil pressure. Yet, sometimes, the check engine light may not light up when your car’s performance decreases or a component gets damaged.

So, why is there no check engine light, but the car runs rough? There could be several reasons for this issue, including:

  1. Damaged Oxygen Sensor
  2. Vacuum Leaks
  3. Corroded Spark Plugs
  4. Dirty Throttle Body
  5. Defective MAF sensor

In this article, we will discuss the common reasons why your vehicle may run roughly without the check engine light coming on. So, let’s get started!

no check engine light but car runs rough

No Check Engine Light But Car Runs Rough: Causes & Solution

Below, I have explained the five most common reasons why there is no check engine light, but your car runs rough.

1. Vacuum Leaks

The engine in your car needs 15.4 grams of air to burn 1 gram of fuel efficiently. When there is a vacuum leak in your car, it allows extra air to enter the engine. Therefore, the idle air control valve struggles to maintain the correct air intake.

Thus, there is more air than fuel in your car’s engine. It causes your car to run roughly. This happens so quickly that the PCM doesn’t have enough time to activate the check engine light.

Solution

Open the hood of your car and check all the vacuum lines and intake manifold gaskets. For visible leaks, you can easily replace the cracked vacuum tubes with new ones.

However, some leaks are not very visible. Thus, to pinpoint the exact location of the leak, you need to use something flammable. Grab a propane torch and turn on the regulator on it.

Be very careful not to light the torch at this point. Move the torch around the air hose, throttle body gasket, and vacuum lines to identify the source of the leak. Afterward, use a good sealant to seal the cracked spots.

For more information on this process, you can watch this YouTube video.

2. Malfunctioning Mass Air Flow Sensor

The MAF sensor in your car generates a frequency of around 30 Hz when the engine is idling and around 150 Hz when you accelerate.

This frequency changes in relation to the airflow. The ECM monitors this frequency and determines the amount of air going into the engine.

If your car’s MAF sensor is damaged, you will notice these signs:

  • You will notice a significant loss of power.
  • You will hear an engine grinding noise at idle.
  • The needle on the gauge will bounce erratically.

This happens because a malfunctioning MAF sensor disrupts the accurate measurement of the air going into your car’s engine. As a result, the engine stalls.

In some cases, this malfunction may not instantly trigger the check engine light in your car. You might think the check engine light is not working, but that’s not the case.

This happens because the frequency generated by the MAF sensor might not have differed too much from the previous measurements stored in the ECU.

Solution

  • You should use a non-flammable electronic cleaner or CRC Mass Air Flow Sensor Cleaner to clean your car’s MAF sensor. This way you can remove excess dirt, or grease.
  • If cleaning does not fix the issue, you should take your car to a mechanic and replace the bad MAF sensor.

3. Damaged Oxygen Sensor

Oxygen sensors in your car improve fuel efficiency and manage exhaust emissions. If your car idles roughly after the engine warms up, it’s probably due to damaged oxygen sensors.

A damaged oxygen sensor cannot accurately measure the oxygen levels in the exhaust gases. So, the sensor sends an incorrect voltage signal that doesn’t match the actual amount of oxygen in the exhaust. Thus, the ECU either sends an incorrect amount of fuel into your car’s engine.

If there is too little fuel in your car’s engine, it can cause your engine to run roughly. Sometimes, a damaged oxygen sensor might not instantly trigger a check engine light. This happens because the old oxygen sensor cannot rapidly send information about changing oxygen levels in the exhaust to the ECU.

Solution

You should ask your mechanic to replace the faulty oxygen sensor in your car with a wide-band oxygen sensor.

A wide-band oxygen sensor can improve your car’s fuel efficiency by around 8.8% to 11.6%. Additionally, it lowers the emission of hydrocarbon gasses by 19.4%.

4. Corroded Spark Plugs

The faulty spark plugs in your car can cause the following issues:

  • Engine misfires.
  • A loss of power.
  • Damage the pistons, cylinders, and O-rings due to excess vibration.

Furthermore, if the gap between the spark plug isn’t right, it can negatively impact the combustion process in your car’s engine.

The ECU typically generates the check engine light when it detects an incorrect signal or severe electrical failures. However, if the spark plug issues occur randomly, your car’s ECU might not immediately activate the check engine light.

Solution

You should take your car to a mechanic. The mechanic can help you identify the exact spark plug that isn’t functioning properly. Afterward, the mechanic can replace the faulty spark plug with a brand-new one.

5. Carbon Deposits On Throttle Body

The throttle body in your car controls the amount of air that goes into the engine. Over time, carbon deposits can accumulate on the throttle body. Thus, air cannot flow to your car’s engine.

When there is less air than fuel in your car’s engine, the fuel can’t burn completely. This lowers your car’s fuel efficiency and makes it run roughly.

If the throttle body in your car is not fully blocked, some air can still get into the car’s engine. This might be the reason the check engine light does not turn on immediately.

Solution

You should clean the throttle body of your car to remove carbon deposits. Below, I have mentioned how you can clean the throttle body.

Step 1: Open the hood of your vehicle.
Step 2: Take off the front engine cover and the air box assembly.
Step 3: Gently detach the MAF sensor.
Step 4: Unplug the breather hose connected to the air tube below the MAF sensor.
Step 5: Disconnect the vacuum line going to the firewall.
Step 6: Use a screwdriver to remove the bolts around the throttle body. Check for the deposit in the throttle body.
Step 7: Use a throttle body cleaner and a toothbrush to clean the walls of the throttle body.
Step 8: Reattach the throttle body and reconnect the hoses you removed earlier.
Step 9: Turn your key to the ON position. You will hear the throttle body clicking in place. Wait for 15-20 seconds. You will hear another clicking sound as the throttle body readjusts.

Final Words

Overall, there are various reasons your car might run roughly. Some of these include damaged spark plugs, a faulty oxygen sensor, and carbon buildup on the throttle body.

Additionally, problems such as vacuum leaks and a faulty idle air control valve can cause rough idling without turning on the check engine light. This can make it harder for you to identify why your car runs roughly.

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