2014 Mercedes-Benz E350 Has Rough Idle

Fix Rough Idle in 2014 Mercedes-Benz E350 for a Smoother Ride

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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 2014 Mercedes-Benz E350 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 2014 Mercedes-Benz E350 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 2014 Mercedes-Benz E350?

To effectively diagnose a rough idle in your 2014 Mercedes-Benz E350, 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 are often the culprits behind rough idling. A clean air filter is essential for optimal engine performance, so ensure it is free of clogs. Following this, examine the fuel system components, including the fuel filter and injectors, to confirm they are delivering fuel efficiently. Don’t overlook the vacuum hoses; any leaks can significantly disrupt the air-fuel mixture, leading to idle problems. Cleaning the throttle body is also crucial, as a buildup of dirt can hinder airflow. Lastly, check the idle air control valve to ensure it is functioning correctly, as this component regulates the engine's idle speed. By following this structured diagnostic approach, you can identify and resolve the rough idle issue effectively.

What are the common causes of a rough idle in a 2014 Mercedes-Benz E350?

When dealing with a rough idle in your 2014 Mercedes-Benz E350, it's essential to understand the common problems that could be at play. One of the primary culprits is dirty or faulty spark plugs, which can lead to engine misfires and an uneven idle. Additionally, vacuum leaks can significantly disrupt the air-fuel mixture, causing instability in engine performance. Another critical component to check is the mass airflow sensor; if it's malfunctioning, it can throw off the air-fuel ratio, resulting in a rough idle. A clogged fuel filter may also be a factor, as it restricts fuel flow to the engine, impacting its ability to maintain a steady idle. Lastly, issues with the idle air control valve can lead to fluctuations in idle speed. By systematically inspecting these components, you can identify and address the root cause of the rough idle, ensuring your vehicle runs smoothly. Regular maintenance and timely repairs are key to keeping your E350 in optimal condition.

How urgent is it to address the rough idle in my 2014 Mercedes-Benz E350?

Addressing a rough idle in your 2014 Mercedes-Benz E350 is crucial for maintaining both performance and safety. Ignoring this symptom can lead to a cascade of problems, including decreased fuel efficiency and engine misfires, which not only affect your driving experience but can also result in costly repairs down the line. A rough idle often indicates underlying issues such as faulty spark plugs, a clogged fuel filter, or a malfunctioning oxygen sensor, all of which can compromise your engine's health. For DIY enthusiasts, it's essential to recognize that timely intervention can prevent more severe damage and ensure your vehicle runs smoothly. Regular maintenance checks and prompt repairs are key to avoiding significant safety risks and preserving the longevity of your car. Therefore, if you notice a rough idle, consider inspecting the vehicle yourself or consulting a qualified mechanic to diagnose and resolve the issue as soon as possible.

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