2013 Mercedes-Benz S400 Has Rough Idle

Resolve Rough Idle in Your 2013 Mercedes-Benz S400 for a Smoother Ride

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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 2013 Mercedes-Benz S400 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 2013 Mercedes-Benz S400 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 initial diagnostic steps to take for a rough idle in a 2013 Mercedes-Benz S400?

When addressing a rough idle in your 2013 Mercedes-Benz S400, it's essential to adopt a systematic diagnostic approach that prioritizes simpler checks before delving into more complex issues. Start by connecting a diagnostic scanner to your vehicle to retrieve any fault codes, as these can offer immediate insights into potential problems. Next, inspect the spark plugs for wear or fouling, as these components play a crucial role in engine performance. A clean and unobstructed air filter is also vital; ensure it is free from dirt and debris to maintain optimal airflow. Additionally, examine the vacuum lines for any leaks, as these can significantly disrupt the air-fuel mixture, leading to idle irregularities. Don't overlook the fuel system; check the fuel filter and injectors to confirm they are delivering fuel efficiently. Finally, inspect the throttle body for carbon buildup, which can hinder its function and affect idle quality. By following this structured approach, you can effectively identify and address the root causes of a rough idle, ensuring your vehicle runs smoothly.

What are the common problems that could cause a rough idle in a 2013 Mercedes-Benz S400?

When dealing with a rough idle in your 2013 Mercedes-Benz S400, it's essential to consider several common problems that could be affecting your vehicle's performance. 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. Additionally, vacuum leaks can create an improper air-fuel mixture, leading to instability in engine idle. Worn or faulty spark plugs are another frequent issue, as they can cause misfires that contribute to rough idling. A clogged fuel filter may also be at fault, as it restricts fuel flow, impacting engine performance. Furthermore, problems with the idle air control valve can disrupt the engine's idle speed, while a malfunctioning oxygen sensor can adversely affect the air-fuel mixture, resulting in poor engine performance. By identifying and addressing these issues, you can restore smooth operation to your S400 and enhance its overall performance.

How urgent is it to address the rough idle in my 2013 Mercedes-Benz S400?

Addressing a rough idle in your 2013 Mercedes-Benz S400 is crucial for maintaining the vehicle's performance and preventing further complications. A rough idle can indicate underlying issues such as faulty spark plugs, vacuum leaks, or problems within the fuel system, which, if left unattended, may lead to decreased fuel efficiency and engine misfires. These symptoms not only affect your driving experience but can also result in significant damage to engine components over time, leading to costly repairs. Therefore, it is essential to diagnose and resolve these issues promptly. While some DIY enthusiasts may feel confident tackling minor repairs, it is advisable to consult a professional mechanic for a thorough diagnosis, especially if the problem persists. By addressing the rough idle quickly, you can ensure the longevity and reliability of your Mercedes-Benz S400, ultimately saving time and money in the long run.

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