2021 Kia Soul Has Rough Idle

Diagnosing Causes of Rough Idle in Your 2021 Kia Soul and How to Restore Smooth Performance

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Reviewed by
Bo Fader
Written by RepairPal Car Genius
Updated January 14, 2025
0%
21% chance it's the
Spark Plugs
0%
15% chance it's the
Ignition Coil
0%
64% chance it's
Something else
The most common reasons a 2021 Kia Soul has rough idle are a vacuum leak, an issue with the spark plugs, or a problem with the ignition coil.
  • Spark Plugs: Worn or fouled spark plugs can lead to misfires, poor fuel economy, and difficulty starting the engine.
  • Ignition Coil: A faulty ignition coil can cause misfires, rough idling, and difficulty starting the engine due to inadequate spark delivery to the spark plugs.
Proper diagnosis will determine the exact cause of your symptom, saving you money on unnecessary repairs. The diagnostic experts at RepairPal Certified shops have the right tools and experience to solve any symptom.

How much does it cost to fix a 2021 Kia Soul has rough idle?

Common Repairs

The total repair cost will vary based on the condition of your vehicle and the number of repairs needed to fix your symptom. Proper diagnosis will save you money by finding the exact repairs needed to fix your car right the first time.

Brake caliper failure occurs in two different ways, and they create different symptoms.

The caliper can become stuck, in which case it won't release the brake pads. The seized caliper will cause the vehicle to brake constantly on one side, forcing the car to move toward that side. This pulling will be accompanied by a strong odor from one wheel.

Another way calipers fail is by leaking. If the caliper leaks, the brake pedal will feel too easy to push, and will sink all the way to the floor when held. Braking will become less effective the longer this goes on. There may also be brake fluid leaking onto the wheel.

Here are a few common symptoms of worn-out brake pads:

  1. Low brake pad warning light is on: Not all vehicles are equipped with this system, but if yours is, this dashboard indicator light will likely be the first signal it’s time to replace your brake pads.
  2. Brakes start to squeal regularly: This is often one of the first signs of worn brake pads and is caused by a metallic piece built into brake pads for this exact purpose. This part contacts the brake rotor to make a squealing or whining noise when the pads are low.
  3. Brakes make loud grinding noise: If not addressed early enough, your brake pads may get so worn that the metal backing plate of the pad grinds against the metal rotor.
  4. Brake pads look thin: You may be able to visually check your brake pad thickness to determine if they need replacement.

Brake rotors are mainly maintenance free, but when they have been subjected to abnormally hard use, the heat they absorb can cause the metal to turn blue, and cracking to occur. When this occurs, customers often specify they have lost braking power, or the vehicle's brakes are making noise. There may be no symptoms at all related to changing the brake rotors, since it is recommended to change brake rotors on most modern vehicles when performing a standard brake service.

Most often, a brake system inspection will just be a routine portion of manufacturer specified maintenance, and will be performed at mileage intervals. In those cases, there will likely be no symptoms. However, when a brake system makes a funny noise, causes vibration, is hard to use, will not slow the vehicle, prevents the vehicle from driving, makes the vehicle pull to one side, or leaks brake fluid, the vehicle will need a visit dedicated to the inspection of the brake system.

What are the steps to diagnose a rough idle in a 2021 Kia Soul?

When diagnosing a rough idle in a 2021 Kia Soul, it's essential to adopt a systematic diagnostic approach that prioritizes simpler checks before delving into more complex issues. Start by using an OBD-II scanner to check for any error codes, as these can quickly point you toward potential problems. Next, inspect the spark plugs for wear or fouling, as they play a crucial role in engine performance. A clean air filter is also vital; ensure it’s free from dirt and debris to maintain proper airflow. Don’t overlook the possibility of vacuum leaks, which can disrupt the air-fuel mixture—check hoses and connections for any signs of damage. Cleaning the throttle body is another important step, as carbon buildup can hinder airflow and affect idle quality. Additionally, assess the fuel system components, including the fuel pump and injectors, to ensure they are functioning correctly. Finally, examine the PCV valve, as a malfunctioning valve can contribute to rough idling. By following this structured approach, you can effectively identify and resolve the underlying causes of a rough idle, restoring your Kia Soul's performance.

What are the common problems that could cause a rough idle in a 2021 Kia Soul?

When dealing with a rough idle in your 2021 Kia Soul, it's crucial to understand the common problems that could be at play. One of the first areas to check is the air filter; a dirty or clogged air filter can significantly restrict airflow to the engine, resulting in an uneven idle. Additionally, inspect the spark plugs, as worn or faulty plugs can cause misfiring, which directly affects engine performance. Another potential culprit is vacuum leaks, which can disrupt the air-fuel mixture and lead to instability in idling. It's also wise to examine the fuel system for issues such as a clogged fuel filter or a malfunctioning fuel pump, as these can hinder proper fuel delivery. Furthermore, the Mass Airflow Sensor (MAF) plays a critical role in maintaining the correct air-to-fuel ratio, and any malfunction here can lead to rough idling. Lastly, the Idle Air Control Valve (IACV) is essential for regulating engine idle speed; if it's faulty, it can cause significant fluctuations in idle quality. By systematically checking these components, you can identify and address the root cause of the rough idle, ensuring your Kia Soul runs smoothly.

How urgent is it to address the rough idle in my 2021 Kia Soul?

When it comes to your 2021 Kia Soul, addressing a rough idle should be treated as a priority rather than a mere inconvenience. A rough idle can be a symptom of various underlying issues, such as faulty spark plugs, fuel system malfunctions, or air intake problems. Ignoring these symptoms not only risks decreased fuel efficiency but can also lead to engine misfires and potentially severe damage to engine components over time. For DIY enthusiasts, it’s crucial to recognize that timely maintenance and repairs can save you from more significant, costly repairs in the future. While some issues may be manageable at home, it’s advisable to consult a professional mechanic for a thorough diagnosis, especially if the rough idle persists. By addressing this issue promptly, you can enhance the longevity and reliability of your Kia Soul, ensuring it runs smoothly for years to come.

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2021 Kia Soul Rough Idle: Causes & Repair Costs | RepairPal