Many car owners complain that their cars tend to lose power, jerk unexpectedly, or make weird noises while they drive at low speeds. It is tough to pinpoint the main cause of this problem as malfunctions in various internal car components can generate the same symptoms.
So, why does the engine misfire at low RPM? The most common causes of this issue include:
- A malfunctioning oxygen sensor
- A valve cover gasket with leaks
- A damaged PCV valve
In this article, we will discuss the common reasons why your car engine might misfire while you are driving at low speeds. So, let’s get started!
Car Engine Misfire At Low RPM: Possible Causes And Fixes
If you are wondering why your car engine misfires at low RPM, check out the information we have provided below.
The Oxygen Sensors In Your Car Have Malfunctioned
As you drive your car, pressurized exhaust gasses leave the cylinders in your car’s engine through the exhaust manifold. These gasses then reach the oxygen sensor attached to the catalytic converter. The oxygen sensor measures the oxygen levels in the gasses emitted by your car’s exhaust system.
Look at the graph we have provided above. Here, you can see that when oxygen levels are low in the exhaust gasses, the sensor generates a voltage between 800 and 1000 millivolts.
However, when the oxygen level is high, the sensor generates a voltage of around 100-200 millivolts. Your car’s ECU monitors these voltage measurements and delivers fuel to your car’s engine based on these values.
If the oxygen sensor in your car is damaged, it will send incorrect voltage measurements to your car’s ECU. As a result, the ECU won’t be able to provide the correct amount of fuel to your car’s engine for complete combustion. This could cause your car engine to misfire at low RPM.
Solution
If you notice the following issues in your car’s oxygen sensors, you need to replace them:
- The wires inside the sensors are frayed.
- The sensors look bent from the middle.
- The sensors are clogged with carbon deposits.
In such cases, take your car to a mechanic and install new oxygen sensors. As per researchers, you should install wide-band oxygen sensors in your car as they provide the following benefits:
- It improves your car’s fuel consumption by 11.6%.
- It detects the smallest changes in the air and fuel mixture in your car.
- These sensors can also reduce the emission of nitrogen oxide gas by 27.3%.
Leak Has Formed In Your Car’s Valve Cover Gasket
If you notice that the spark plugs in your car are covered in engine oil, it means a leak has formed in the valve cover gasket in your car.
This component acts as a barrier between the valve cover and the cylinder head in your car’s engine. It also includes small circular rubber gaskets that prevent engine oil from entering the spark plugs in your car.
When you drive your car at low RPM, it needs a strong spark to burn the air and fuel mixture properly. However, if the valve cover gasket and the gaskets around the spark plug housing in your car have developed a leak, the engine oil will enter in the spark plugs.
Thus, the spark plugs in your car won’t be able to generate a strong spark to ignite the fuel and oxygen mixture in your car’s engine. So, your car’s engine will misfire at low RPM.
Solution
You should take your car to a good mechanic and ask the mechanic to inspect the degree of damage the valve cover gasket in your car has sustained.
If the valve cover gasket has small cracks, the mechanic can seal them with a sealant. But, if the leak is huge, the mechanic needs to replace the entire rubber gasket with new ones.
The PCV Valve In Your Car Has Failed
The PCV valve in your car ensures that contaminated exhaust gasses leave your car’s crankcase and enter the inlet manifold in your car. There, these gases are burned with the air and fuel mixture in your car’s engine.
Thus, the PCV valve in your car provides the following benefits:
- It helps to remove the moisture that collects in your car’s crankcase.
- It stops contaminated gasses from entering your car’s engine.
- It prevents extra pressure from building up inside the crankcase.
- It allows fresh air to flow through your car’s engine.
When you drive your car at low speeds, the vacuum inside your car’s engine stays low. So, the PCV valve in your car closes a bit to reduce the airflow from the crankcase. This allows the right amount of air to enter your car’s engine to burn the fuel.
But if the PCV valve is damaged, it can’t do this job properly. This means an incorrect amount of air might enter your car’s engine. As a result, your car’s engine could misfire.
Solution
If your car’s PCV valve is damaged, you should install a new PCV valve in your car. Read the steps we have given below to learn how to install a PCV valve.
- Step 1: Open the hood of your car.
- Step 2: Try to locate this valve near the valve cover in your car’s engine.
- Step 3: Disconnect the vent hose that goes to your car’s intake manifold.
- Step 4: Gently twist the valve to remove it from its original position.
- Step 5: Attach the new PCV valve in place of the damaged one by turning it clockwise.
- Step 6: Press the valve with your thumbs to secure it tightly in place.
- Step 7: Reconnect the vent hose to the intake manifold.
- Step 8: Lastly, check all the connections again and close the hood of your car.
For a visual representation of this process, you can watch this YouTube video.
Why does an engine misfire at high RPM? You might find our article on ‘Engine Misfire at High RPM: Diagnosis and Solutions’ helpful; it covers everything you’ll ever need. Engine Misfire at High RPM provides an in-depth examination of why an engine misfire happens at high RPM. Meanwhile, our article on Can a Bad Alternator Cause a Misfire? explores all the crucial aspects related to this issue.
FAQs
To gain more information on why car engine misfires at low RPM read the FAQs we have given here.
Q: What should I do to prevent my car engine from misfiring while driving at a slow speed?
You should ensure that your car’s internal components, like spark plugs, ignition coil, PCV valve, and oxygen sensors, are in good condition. Furthermore, you should put high-quality fuel in your car and avoid roughly driving your vehicle.
Q: How often should I change spark plugs to prevent engine misfires from worn-out plugs?
After you have traveled 30,000 kilometers to 50,000 kilometers in your car, you should change the spark plugs. This is because extended use of aftermarket spark plugs can cause them to wear out. So, damaged spark plugs will generate weak sparks that may cause your car engine to misfire.
Overall, the engine in your car can misfire at low RPM for various reasons. However, car owners often experience this issue when internal car components become damaged, corroded, or develop leaks.
Such components include the oxygen sensor, spark plugs, PCV valve, and valve cover gasket. Therefore, you should check the condition of these elements every few months and replace them promptly if they show any signs of malfunction.