2019 Mercedes-Benz GLC300 Has Rough Idle

Troubleshooting Causes of Rough Idle in Your 2019 Mercedes-Benz GLC300 and How to Resolve Them

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Reviewed by
Devin Cabugcal
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 2019 Mercedes-Benz GLC300 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 2019 Mercedes-Benz GLC300 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 2019 Mercedes-Benz GLC300?

When diagnosing a rough idle in a 2019 Mercedes-Benz GLC300, it's crucial to follow a structured diagnostic approach that begins with the simplest checks and progresses to more complex issues. Start by utilizing a diagnostic scanner to retrieve any fault codes from the vehicle's computer system, as these codes can provide immediate insights into potential problems. Next, inspect the spark plugs for signs of wear or fouling, since their condition directly impacts engine performance. After that, evaluate the air intake system for leaks or clogs that could disrupt the air-fuel mixture, which is vital for smooth operation. It's also essential to examine the fuel system components, including the fuel filter and injectors, to ensure they are delivering adequate fuel. Pay attention to the vacuum hoses as well; any leaks or disconnections can significantly affect engine performance. Additionally, inspect the throttle body for carbon buildup, which can impair idle quality. Lastly, assess the engine mounts for any signs of wear, as damaged mounts can lead to vibrations that contribute to a rough idle. By systematically addressing these areas, you can effectively diagnose and resolve the rough idle issue in your GLC300.

What are the common problems that could cause a rough idle in a 2019 Mercedes-Benz GLC300?

When diagnosing a rough idle in a 2019 Mercedes-Benz GLC300, it's essential to consider several common problems that could be affecting the vehicle's performance. One of the primary culprits is a dirty or faulty mass airflow sensor, which can disrupt the delicate balance of the air-fuel mixture necessary for smooth engine operation. Additionally, vacuum leaks can create an imbalance in this mixture, leading to an unstable idle. Worn or faulty spark plugs are another frequent issue, as they can cause misfires that result in a rough engine idle. A clogged fuel filter may also restrict fuel flow, further contributing to performance issues. Furthermore, problems with the idle air control valve can disrupt the engine's idle speed, while a malfunctioning oxygen sensor can negatively impact the air-fuel mixture, exacerbating rough idling. By understanding these potential issues, DIY enthusiasts can take proactive steps in troubleshooting and maintaining their GLC300, ensuring a smoother driving experience.

How urgent is it to address the rough idle in a 2019 Mercedes-Benz GLC300?

Addressing a rough idle in your 2019 Mercedes-Benz GLC300 is not just a matter of comfort; it is crucial for the longevity and performance of your vehicle. A rough idle can indicate underlying problems such as dirty fuel injectors, a clogged air filter, or faulty spark plugs, which, if left unattended, can lead to more severe issues like engine misfires and decreased fuel efficiency. Ignoring these symptoms may result in significant damage to engine components over time, potentially leading to costly repairs. Therefore, it is essential to act promptly when you notice a rough idle. By diagnosing and resolving the issue early, you can maintain your vehicle's optimal performance and avoid the risk of safety hazards associated with engine malfunctions. Taking the time to address this concern will not only enhance your driving experience but also protect your investment in the long run.

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2019 Mercedes-Benz GLC300 Rough Idle Troubleshooting