Car Starts Rough: Possible Vehicle Causes and Fixes

If your car starts rough, you’re likely dealing with a case of rough idling. Several culprits are responsible for your car starting roughly; the most common is a faulty spark plug.

Car Starts Rough Reasons and Remedies

A car that rough starts will have a potentially devastating effect on the engine. Our automobile team help you identify the main reasons why your car rough idles and how to troubleshoot this problem.

What Are the Most Common Casues of Your Car Starting Rough?

The most common causes of your car starting rough include a defective spark plug, a defective ignition system, and a blown head gasket. These and several other issues associated with the car’s battery can cause your car to have a rough start.

Your car is rough idling due to a defective idle valve control and a leak in the vacuum pipe. A defective fuel injection system, jammed fuel filters, faulty air meter, and bad CTS can also cause your vehicle to idle roughly.

– Bad Spark Plugs

Spark plugs are one of the most vital components of a car. They work by igniting your fuel and air mixture to power your pistons. As small as they are, they can affect your vehicle’s performance if they’re worn or bad. Faulty plugs will cause your car to misfire when you accelerate, which can cause your car to start rough.

When you’re dealing with bad plugs, there are signs that point out this defect. Aside from your car starting rough, you may also notice sputtering or rattling noises coming from your car. Your vehicle’s performance will also drop, and there will be a decrease in fuel mileage.

How can you identify a faulty spark plug?

You can tell if your plug is broken when your engine starts to misfire or stall. Other signs of a broken plug include a decrease in the engine’s performance and power and poor gas mileage. You may also notice unusual noises and difficulty in starting your engine.

– Broken Carburetor

Often found in older vehicles, a carburetor supplies air/fuel mixture to an internal combustion engine. If your carburetor is broken, it will affect your car’s performance. You may experience difficulty starting your car. It also affects the proportion of the air/fuel mixture that gets into the engine.

What Are the Most Common Casues of Your Car Starting Rough

It causes the engine to overwork itself, leading to reduced engine power. Other signs of a broken carburetor include poor gas mileage, increased exhaust smoke, engine overheating, and misfiring.

– Clogged Fuel Injectors

Clogged or dirty fuel injectors are another common cause of a rough idle. A fuel injector performs the crucial role of spraying fuel into an air mixture to aid proper combustion. This injector can become clogged due to an accumulation of soot, grime, and dirt.

When this happens, there will be an imbalance in the fuel that goes into the combustion cylinders. One of the obvious signs of a faulty injector is that your car begins to start roughly or stall unnecessarily.

Other tell-tale signs are a decrease in fuel economy, engine misfiring, and unusual noises. Your check engine light will likely come on at this point, and you may notice the needle in your tachometer moving weirdly.

– Vacuum Leaks

A vacuum leak might be the culprit if you have trouble starting your car smoothly. When your vacuum pump is bad, it can disrupt the proper fuel-air ratio needed for combustion.

Such a leak will surely affect the performance of your engine since more air and less fuel are coming into the combustion cylinder.A leak in the vacuum also prevents the EGR valve and the PCV valve from functioning properly.

In this case, the engine starts to overheat, which will, in turn, cause it to stall or misfire, leading to a rough start. A leak in your vacuum can also affect your AC performance and brakes and produce a hissing sound.

– Defective Temperature Sensor

A coolant temperature sensor (CTS) communicates the engine’s temperature to the engine control module (ECM). When your sensor is bad or faulty, it provides incorrect information to your ECM.

The engine control module then adjusts the fuel-air ratio, engine idle speed, and ignition timing to match its received information. However, these adjustments will not match the actual operating temperature of the engine, which can cause your vehicle to have a rough start.

– Bad IAC Valve

The idle air control valve works hand in hand with the engine control module to regulate airflow into the engine. The biggest sign of a bad IAC system is that your car will start idling rough. You may also notice that your engine stalls or backfires during operation. In extreme cases, your engine will refuse to start.

– Faulty MAF Sensor

A mass air flow sensor, also known as an air meter, plays an important role in your engine. It measures the amount of air that flows into your engine. The air meter helps improve your engine’s performance by allowing your ECM module to supply the right fuel.

As such, a faulty air meter will greatly affect an engine’s performance.An obvious symptom of a bad air meter is that your car will rough idle or stall unnecessarily. Your engine will produce lesser power, which limits the operation of the vehicle.

You may also notice a clunking or sputtering noise from your engine whenever it starts. Black smoke from the exhaust is another sign associated with a bad air meter.

– Blown Head Gasket

A blown head gasket is another common cause of a car starting rough. A head gasket prevents the mixture of engine oil and coolant. It also seals the combustion chamber to improve compression and prevent combustion gases from flowing out to other passages.

If your head gasket is blown, it creates an imbalance in compression, which will cause your engine to idle roughly. Aside from the difficulty in starting your car, your engine will start overheating.

You’ll also notice white smoke coming from your tailpipe. Your coolant level will significantly drop, and the engine oil will be contaminated.

– Damaged Ignition Coils

Another reason your car idles rough is that you are probably driving with damaged coils. An ignition coil converts low current from the car battery to high current needed to ignite fuel for movement.

Once you experience difficulty starting your engine or a rough idle, it may indicate a problem with your coils.Engine misfiring is another sign of damaged coils and reduced engine performance.

All of these signs indicate that your coils need replacement. If you want to be certain, you can get a diagnosis from a professional mechanic.

– Clogged Air Filters

Although easily overlooked, clogged engine filters can cause your car to start rough. An engine filter rids incoming air of dirt, particles, and dust that can disrupt combustion once they get into the engine.

Symptoms of Clogged Air Filters

A working filter improves the engine’s generation of horsepower and fuel efficiency. When your filters are clogged, your engine’s performance reduces due to contaminants in the airflow.It becomes difficult to start your car smoothly or accelerate without jerks.

Another sign of a clogged filter is that it decreases your gas mileage. You’ll also notice a sulphuric, fuel-like odor inside your car’s cabin anytime you start the engine. Unusual noises and black smoke from the exhaust system are also signs of a clogged filter.

– Low Battery Charge in Cold Weather

One common reason your car may start roughly in cold weather is due to low charge from the battery. During the cold season, the chemical process of a battery is reduced. When this happens, the battery produces a low charge capable of generating enough power for the engine. Other reasons include worn plugs, a defective ignition system, and a bad air meter.

– Defective Fuel Pump

The signs of a bad fuel pump are stalling and sputtering noises from the engine compartment. Other signs of a defective gas pump include trouble starting the engine and the smell of fuel in the vehicle’s cabin. You may also notice your engine warning light flashing on your dashboard.

What Should You Do if Your Car Starts Rough?

If your car starts rough, you can try replacing the plugs, coils, and CTS to eliminate the car’s problem of starting roughly. You can also repair or replace your IAC, and if you need clarification on the problem, you can consult a professional mechanic.

– Use An Error Code Scanner

An error code scanner is essential in detecting the cause of a rough start. To use an error code scanner, you must first connect it to the vehicle’s diagnostic port, which is located under the dashboard.

After connection, the scanner will immediately display error codes stored in the car’s computer. Different error codes represent a specific error, so you may need a professional to decipher what each error code means.

– Replace the CTS

Replacing your bad coolant sensor is one of the quickest ways to troubleshoot the problem of a car rough idle. Although you should seek the help of a professional technician, replacing a CTS is relatively easy. First, locate the sensor, which is usually close to the thermostat housing or the engine block.

Remedies of Car Starts Rough


You should carefully disengage the connector cable that connects the sensor to the vehicle’s harness. The next step is to remove the sensor from its socket by turning it clockwise and removing all bolts and clips. Install the new sensor, ensuring it’s held in place by a torque wrench.

Clean the connector cable of all dirt or grime before reinstalling the connector cable to the new sensor. Start the engine to test the new sensor and ensure it gives accurate temperature readings.

– Replace the IAC System

Another step in the right direction to eliminate rough starts is to replace your IAC system. Before replacing an IAC system, you must disconnect the battery from the negative cable.

You should locate the IAC system close to the intake manifold, although it depends on your vehicle’s model and brand. Use a plier to disconnect the electrical harness that connects to the valve.

After that, remove the bolts holding the valve to the mounting bracket and remove the old valve. Clean the mounting bracket with a throttle body cleaner to eliminate contaminants and create a clean seal. Install the new valve and reconnect the electrical harness.

After that, reconnect the negative battery cable to the battery and ensure all bolts are tightened properly. Start your engine and test it for idle speed to ensure it runs smoothly.

– Replace the Air Meter

Turning off your car’s battery is the first step in replacing your damaged air meter. Locate the air meter, which is usually close to the air intake duct or air filter box. In some car models, you may need to remove the air intake duct or filter box to access the air meter. Disconnect the electrical connector by squeezing the harness tab on the side of the connector.

Remove the defective air meter and install the new one, ensuring the clamps and bolts are in place. Reconnect your battery and test the new air meter to ensure that you installed it properly.

– Fix Leaks in the Vacuum

If left unchecked, a leak in your vacuum can permanently damage your engine. The first thing to do when trying to fix a leak is to inspect the vacuum for visible damage. If there’s none, start your engine and listen for any whistling or unusual sound.

If you hear nothing but are certain of a leak, you can use a vacuum gauge to check the vacuum line readings.Also, check the hoses and connectors for cracks and fix these if damaged. You may also need to inspect your intake manifold gasket for leaks, cracks, and damage and replace it if needed.

You should also inspect all vacuum valves for damage and replace them. After making all necessary repairs, test the vacuum system to be sure it functions properly.

– Replace the Ignition System Component

A faulty ignition system disrupts the smooth performance of your vehicle. Replacing the defective component is a step towards eliminating the issue of your car starting roughly. The first thing you should do is disconnect the battery for personal and vehicular safety.

Locate the ignition system, which is usually close to the engine block. Once you’ve located the system, disconnect the connectors and bolts holding it in place. Install the new ignition component and reconnect all connectors and harnesses.

After installation, start your engine and check for misfiring, jerks, and unusual noises. You may have successfully installed a new ignition component if you notice nothing weird.

It is important to note that these steps may differ depending on your car brand and model. Consult your owner’s manual for specific instructions on locating each component. Finally, consult a car repair professional if you need to gain more technical knowledge of automobile repairs.

– Go to the Mechanic

It is time to go to a mechanic when you notice an odd change in your vehicle’s operation. You don’t have to wait for the problem to be severe before consulting a mechanic. Once you notice two or more of the symptoms discussed above, it is time to visit a mechanic.


– Is Driving a Car With Rough Start Safe?

No, it isn’t safe to drive a rough car. If your car rough idles and it seems severe, driving can be hazardous, especially as you have no control over its operation. Your car could misfire, rev, or stall unexpectedly, which can lead to a crash especially on a highway.

Conclusion of Car Starts Rough Possible Vehicle Causes and Fixes


Experiencing a rough start indicates an issue with some components of your car.

Here’s a quick recap of the key points discussed in this article:

  • Your car starts rough due to worn plugs and coils, a faulty air meter or CTS, and a leak in your vacuum pipes, among others.
  • You can resolve this issue by replacing your plugs, ignition components, or air meter.
  • An error code scanner is a handy tool for discerning your car’s defects. You have to connect this scanner to your vehicle’s diagnostic port, which is located underneath the dashboard.
  • You can consult a professional mechanic, an owner’s manual, or an error code scanner to determine the problem and where some components are located.

In conclusion, a car starting roughly can be caused by several factors. Once you identify the cause, you should fix it immediately to avoid further complications.

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