2019 Mercedes-Benz C300 Has Rough Idle

Troubleshooting Causes of Rough Idle in Your 2019 Mercedes-Benz C300 and How to Resolve Them

Find Repair Location
Reviewed by
Aisha
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 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 2019 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.

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.

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 C300?

When diagnosing a rough idle in a 2019 Mercedes-Benz C300, it's essential to adopt a systematic diagnostic approach that prioritizes simpler checks before delving into more complex issues. Start by using a diagnostic scanner to check for fault codes, as these can quickly point you to specific problems within the vehicle's systems. Next, inspect the spark plugs for wear or fouling, as these components play a crucial role in engine performance. A clean air filter is also vital; ensure it is free from clogs that could restrict airflow. Following this, examine the fuel system, including the fuel filter and injectors, to confirm that fuel delivery is optimal. Don’t overlook the vacuum hoses; any leaks can significantly affect engine idle. Additionally, inspect the throttle body for carbon buildup and check the mass airflow sensor for cleanliness and functionality. By methodically addressing these areas, you can effectively identify and resolve the underlying causes of a rough idle, ensuring your vehicle runs smoothly.

What are the common problems that could cause a rough idle in a 2019 Mercedes-Benz C300?

When dealing with a rough idle in your 2019 Mercedes-Benz C300, it's essential to understand the common problems that could be at play. One of the primary culprits is a dirty or faulty mass airflow sensor, which can disrupt the delicate balance of air and fuel entering the engine, leading to an uneven idle. Additionally, vacuum leaks in the intake system can introduce unmetered air, further complicating the air-fuel mixture and causing instability in engine performance. Worn or faulty spark plugs are another frequent issue, as they can lead to misfires that manifest as a rough idle. A clogged fuel filter may also be a factor, as it restricts fuel flow, impacting the engine's ability to maintain a smooth idle. Furthermore, problems with the idle air control valve can disrupt the engine's idle speed, while a malfunctioning oxygen sensor can throw off the air-fuel mixture, exacerbating the rough idle. By identifying and addressing these common issues, you can restore your vehicle's performance and enjoy a smoother driving experience.

How urgent is it to address the rough idle in my 2019 Mercedes-Benz C300?

Addressing a rough idle in your 2019 Mercedes-Benz C300 is not just a matter of comfort; it is crucial for the overall health and performance of your vehicle. Ignoring this symptom can lead to serious engine problems, such as misfiring cylinders or fuel system malfunctions, which may escalate into costly repairs if left unattended. Additionally, a rough idle can significantly reduce your car's fuel efficiency, resulting in higher fuel costs over time. The vibrations and noise associated with a rough idle can detract from your driving experience, making it uncomfortable and distracting. Moreover, unresolved issues can lead to increased emissions, potentially causing your vehicle to fail environmental standards. Therefore, it is essential to prioritize addressing a rough idle promptly to safeguard your engine's longevity, enhance fuel efficiency, and ensure a smooth, enjoyable ride.

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.