2024 Mercedes-Benz C300 Has Rough Idle

Resolve Rough Idle in 2024 Mercedes-Benz C300 for a Smoother Ride

Find Repair Location
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 2024 Mercedes-Benz C300 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 2024 Mercedes-Benz C300 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 2024 Mercedes-Benz C300?

When diagnosing a rough idle in a 2024 Mercedes-Benz C300, it's crucial to follow a structured diagnostic approach that begins with simpler checks before moving on to more complex issues. Start by connecting a diagnostic scanner to the vehicle's computer system to retrieve any error codes, as these can quickly highlight potential problems. Next, inspect the spark plugs for signs of wear or fouling, since these components are vital for proper ignition and can significantly impact engine performance. After that, evaluate the air intake system, including the air filter and mass airflow sensor, to ensure there are no blockages that could disrupt the air-fuel mixture. It's also essential to check the fuel system for adequate pressure and ensure that the fuel injectors are functioning correctly, as any issues here can lead to a rough idle. Additionally, examine the vacuum hoses for leaks, which can adversely affect air intake, and test the ignition system components to confirm they are operating as intended. Lastly, inspect the EGR valve to ensure it is functioning properly, as a malfunctioning EGR valve can also contribute to rough idling. By systematically addressing these areas, you can effectively diagnose and resolve the rough idle issue in your vehicle, ensuring optimal performance.

What are the common problems that could cause a rough idle in a 2024 Mercedes-Benz C300?

When dealing with a rough idle in your 2024 Mercedes-Benz C300, it's crucial to consider several common problems that could be at play. One of the primary culprits is dirty or faulty spark plugs, which can lead to engine misfiring and an uneven idle. Additionally, vacuum leaks can disrupt the delicate air-fuel mixture necessary for smooth engine operation, resulting in a rough idle. Another potential issue is a malfunctioning mass airflow sensor, which can hinder the engine's air intake and affect performance. A clogged fuel filter may also be a factor, as it restricts fuel flow to the engine, impacting idle quality. Furthermore, a faulty oxygen sensor can cause incorrect air-fuel mixtures, contributing to rough idling. Lastly, problems with the Exhaust Gas Recirculation (EGR) valve can significantly affect engine performance, including idle stability. By identifying and addressing these issues, you can restore optimal performance to your Mercedes-Benz C300 and enjoy a smoother driving experience.

How urgent is it to address the rough idle in my 2024 Mercedes-Benz C300?

Addressing a rough idle in your 2024 Mercedes-Benz C300 is not just a matter of comfort; it is crucial for the overall health of your vehicle. A rough idle can signal serious underlying problems within the engine, fuel system, or ignition system, which, if ignored, may escalate into more significant issues that could compromise your vehicle's performance and safety. Neglecting this symptom can lead to decreased fuel efficiency and increased emissions, not to mention the risk of damaging vital engine components, which can result in costly repairs. Therefore, it is essential to prioritize diagnosing and resolving a rough idle promptly. By doing so, you not only enhance your driving experience but also safeguard your investment in your vehicle, ensuring it remains in optimal condition for the long haul.

You’ve got options with RepairPal

Whether you need a more accurate auto repair estimate or help finding a reputable shop in your area, we’ve got you covered.

2024 Mercedes-Benz C300 Rough Idle Causes & Repairs