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Car Idling Rough: What Causes it and How Can You Fix it? 

Car Idling Rough

A car idling rough is a common issue and is caused by a number of factors. You will know that there is a problem when your car is rather bouncy and rough while the engine is running. It is not how it’s supposed to operate. What causes a car idling rough? Will we be able to fix it? 

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Car Idling Rough: What causes a rough idle?


To understand what takes place when you see your car idling rough, we have to learn the basics first. When you idle your car, it would mean that the engine is running without you stepping on the accelerator or putting it into gear, right? When you do this, a smooth and healthy idling should have a steady but low rate of revolutions with its tachometer being steady, too. It should be able to supply enough power to operate the basic system of your car like the electrical system and power steering. 


You may have a problem when your car doesn’t feel like that or when you feel your car idling rough. You can feel it when your car seems to have a difficulty maintaining a steady rate of rotation or feel it rising and falling. If these things start to happen, you will need to have your car checked since there is a problem somewhere in there that needs to be repaired. 


So what are the causes of a car idling rough? Here are some of its most common causes.

  • The fuel injector is dirty.


The vehicles today are equipped with engines that are very fuel-efficient. They use high-pressure fuel injectors that spray fuel into the car’s engine. They operate using electronic controlled valves that are very capable of opening and closing many times per second. They could precisely spray the right amount of fuel at the right moment into each cylinder. 


These fuel injectors, no matter how very capable they are in doing their task efficiently, they are still prone to contaminations and such. They get dirty or clogged over time since the injectors have spray nozzles that have tiny openings. When this happens, less fuel will be supplied that can cause rough idling of your car.


How to fix it:


If the problem hasn’t been diagnosed yet, it is recommended that you have it diagnosed by a repair shop that has an exhaust gas analyzer. This is because damaged injectors have high carbon monoxide and hydrocarbon readings. 


If it has already been checked and simple cleaning can fix the problem, you can ask a mechanic to clean your fuel injector. Mechanics have injectable cleaning concentrate that they use to clean them out. 


You can also use an injector cleaner gas additive to clean your fuel injectors before they start to give you problems. Remember that gas additives are best used as a preventive measure and it may or may not help your car idling rough problem.


  • Vacuum leaks.


Many vehicles have a number of hoses that create a vacuum seal for the fuel and the air. It is controlled by a throttle to regulate the airflow and the engine speed. Without it, your car will not be supplied with air and fuel mixture which is necessary to produce combustion. The vacuum is the difference in pressure between the outside air pressure and the interior of the intake manifold.   


Vacuum leaks, in automotive language, mean that a specific amount of air has bypassed the usual engine intake tract. It is not supposed to happen. All of the intake air of the engine should always be routed through the throttle body because inside it is where the quantity of air going to the engine is being measured by the mass air-flow sensor. 


When a vacuum leak happens, a certain amount of air enters into the intake manifold without passing through the said throttle body which causes the ECU or engine control unit to inject the needed amount of fuel based solely on the data received from the air-flow sensor. This causes a lean air-fuel mixture that could result in a car idling rough and slow acceleration. 


Vacuum leaks can happen when the hoses are worn out or cracked due to exposure to extreme temperatures. A broken rubber tube connected to the intake manifold can also cause a vacuum leak. 


How to fix it:


There are several ways to spot a vacuum leak but a visual check is always a good way to start. Check the rubber and plastic vacuum hoses for any damages like cracks. It is best to check these components while the engine is running. 


Once you know the source of the leak, it can be an easy fix. Damaged rubber hoses, sensors, valves, and tube O-rings are easy to replace and they won’t cost you that much. If the vacuum leak is not caused by these faulty components but rather by a bad intake manifold gasket or brake boosters, you better have it checked and fixed by a professional. 

  • Spark plugs are worn out.


Another possible reason why you experience a car idling rough is because of worn-out spark plugs. With the help of the ignition coil that produces high voltage, the spark plugs create a spark that ignites the fuel and air mixture in each cylinder of your engine. 


Spark plugs get faulty over time due to the carbon build-ups, dirt, or oil from the combustion process. When this happens, the amount of power produced when the spark plug ignites decreases. Spark plugs that are not maintained and changed on schedule – conventional spark plugs have to be changed every 30,000 to 50,000 miles – can lead to worn electrodes. This creates a larger gap that requires more power to operate which can potentially damage other components. These problems can lead to a rough idle and other engine-related problems.  


How to fix it:


You can remove your spark plug and inspect its condition to know why your car is idling rough. If you see carbon deposits, it means that the spark plug is not strong enough. If you see oil deposits, it could mean that the valves are leaking or the piston rings are faulty while an ash deposit means that your oil is leaking or perhaps you are using low-quality fuel.


You can also check your spark plug wires since they can be the reason for a rough idle. You will have to replace them if they are faulty. 

  • Clogged air filter.


The car’s air filter is the one that keeps the dust, dirt and other foreign substance from entering the engine. It is recommended that car owners should replace their filters at least once a year since most car air filters use a folded paper element that can get clogged if not changed regularly. 


If the filter is clogged, the flow of air into the engine will be reduced and this could cause a car idling rough and a poor fuel economy. Keep in mind that your car needs air as much as it needs fuel.


How to fix it:


You will need to replace your air filter to fix the issue. Remove the old one and replace it with a new air filter. Clean the filter housing of any dirt build-up while you’re at it.

  • Faulty fuel pump and clogged fuel filter.


A car idling rough can be caused by some fuel delivery issues. If the engine doesn’t get enough fuel, it could result in a rough idle, stalling, sputtering, and slow acceleration. This can happen when the fuel pump is defective or clogged since it is the one that pulls the fuel from the tank into the fuel injectors. 


A clogged fuel filter can also cause similar problems. It filters foreign matter in the fuel. It gets clogged over time and when it happens, the engine won’t be able to receive enough fuel. 


How to fix it:


To fix the issue, you can have your fuel pump cleaned, fixed, or even replaced depending on the severity of the issue. Clogged fuel filters have to be replaced with new ones. Experts say that car owners should replace fuel filters regularly to help prolong the fuel pump’s life. Check your owner’s manual for the recommended interval. 

  • Dirty oxygen sensor.


Car idling rough can be caused by a dirty oxygen sensor. It is one of the many types of sensors found in a car and its job is to measure how rich or lean the gases are when they exit the combustion chamber. Based on the results, the car’s computer will adjust the amount of fuel that enters the engine.


A dirty or faulty oxygen sensor can send incorrect data to the car’s computer. This can cause the engine to run too rich or too lean which can result in a car idling rough.  


How to fix it: 


You will know that your oxygen sensor needs cleaning when you see the check engine light turned on and by using your OBD-II scanner and checking the trouble codes. 


To fix the issue, you need to clean your oxygen sensor by using a commercial product intended for emission system cleaning and follow its instructions. Keep in mind that you should never use non-automotive solvents or cleaning products. 

  • Carburetor problems.


Old car idling rough can be a result of having carburetor problems. Older cars with higher mileage can encounter this problem. One indication that the rough idling is caused by carburetor problems is when you see thick, black exhaust smoke when the engine is running. A healthy carburetor shouldn’t emit black smoke and seeing one only means that there is something wrong with it. 


How to fix it:


You can fix it by cleaning your carburetor by using a carburetor cleaner. It is a simple solution that can help you clean carbon build-ups and other contaminants. Keeping your carburetor clean can help prevent a car from idling rough.


You can also check the choke whether it is fully opened when the engine has warmed up or not. If you see it fully open, the problem might be caused by some internal issues that might require a carburetor rebuild to be fixed.  

Car Idling Rough: Is it safe to drive a car with a rough idle?


Car idling rough is not its normal operating condition. It is caused by a variety of problems that need to be addressed immediately. You can drive it but don’t wait too long before you have it checked and repaired to prevent a much worse problem and before it becomes too expensive to fix. There are some diagnostic tests you can do yourself to determine the problem but if you are not that confident and lack mechanical skills, you better have a mechanic check and diagnose your car for you.  


You should also consider noting the exact circumstances where you feel or notice your car idling rough. This can help you or your mechanic narrow down what causes it. It can help you save time and money too. You need to know whether your car idles rough when you start or warm it up, or if strange noises come along with it. Take note of everything you notice when it happens. 


Car Idling Rough: Final Word


Keep in mind that a healthy engine should run smoothly without any noise and problem. A car idling rough can be noticed at first since it can cause you inconvenience and alarm but it is more than that. It is caused by a number of problems and you need to have it checked and correct it immediately. It can only be the beginning of a more serious problem if you don’t act fast.


Take note of how your car idles. You can tell its overall condition just by observing it. If it is smooth and doesn’t have excess noise, it is a good indication. If your car is idling rough, bouncy, or noisy, then it’s another story. Plan or set a schedule and have it checked as soon as possible.  

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