2016 Mercedes-Benz SL400 Has Rough Idle

Resolve Rough Idle in 2016 Mercedes-Benz SL400 for a Smoother Ride

Find Repair Location
Reviewed by
Andrew Hajjar
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 2016 Mercedes-Benz SL400 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 2016 Mercedes-Benz SL400 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 2016 Mercedes-Benz SL400?

To effectively diagnose a rough idle in your 2016 Mercedes-Benz SL400, start with a systematic approach that prioritizes simpler checks before delving into more complex diagnostics. Begin by using a diagnostic scanner to check for any fault codes, as these can quickly point you to underlying issues. Next, inspect the spark plugs for wear or fouling, as these components are crucial for proper engine performance. A clean air filter is essential for optimal airflow, so ensure it is free from debris. Don’t overlook the vacuum hoses; any cracks or leaks can significantly impact engine idle quality. Additionally, examine the fuel system, focusing on the fuel filter and injectors, since blockages here can lead to rough idling. Testing the mass airflow sensor is also vital, as a malfunction can disrupt the air-fuel mixture. Finally, inspect and clean the throttle body to remove any carbon buildup that may be affecting its function. By following this structured diagnostic approach, you can effectively identify and resolve the rough idle issue in your vehicle.

What are the common problems that could cause a rough idle in a 2016 Mercedes-Benz SL400?

When dealing with a rough idle in your 2016 Mercedes-Benz SL400, 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-out spark plugs or malfunctioning ignition coils are also significant factors, as they can lead to misfires that manifest as a rough idle. Another potential issue is a clogged fuel filter, which restricts fuel flow and can severely impact engine performance at idle. Furthermore, problems with the idle air control valve can disrupt the engine's idle speed, while a malfunctioning throttle body can hinder proper air intake. By identifying and addressing these issues through regular maintenance and timely repairs, you can restore smooth idling to your vehicle, ensuring a more enjoyable driving experience.

How urgent is it to address the rough idle in a 2016 Mercedes-Benz SL400?

Addressing a rough idle in your 2016 Mercedes-Benz SL400 is not just a matter of comfort; it is crucial for the overall health of your vehicle. A rough idle can indicate serious underlying problems, such as faulty spark plugs, fuel system malfunctions, or issues with the air intake. Ignoring these symptoms can lead to decreased fuel efficiency and engine misfires, which may escalate into more severe damage over time. Moreover, a rough idle can compromise your vehicle's performance, making it less reliable and potentially unsafe to drive. Regular maintenance and prompt repairs are essential to avoid costly repairs in the future. Therefore, if you notice your SL400 idling roughly, it is imperative to diagnose and address the issue as soon as possible, ideally with the help of a qualified mechanic, to ensure your vehicle remains in optimal condition.

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.