Mercedes-Benz ML350 Has Rough Idle

Diagnosing the Causes of Rough Idle in Your Mercedes-Benz ML350 and How to Resolve Them

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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 Mercedes-Benz ML350 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 Mercedes-Benz ML350 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.

Troubleshooting Rough Idle in a Mercedes-Benz ML350

When troubleshooting a rough idle in your Mercedes-Benz ML350, it's essential to adopt a methodical diagnostic approach. Begin by checking for vacuum leaks, as these are often the root cause of idle issues. Inspect the vacuum hoses for cracks or disconnections, which can lead to an unstable air-fuel mixture. Next, examine the ignition coils; signs of wear or failure can manifest as rough idling and should be replaced if necessary. After addressing these simpler fixes, assess the condition of engine mounts and other components for wear and tear, as these can also contribute to a shaky idle. Additionally, consider cleaning or replacing the EGR valve, air filter, MAF sensor, and spark plugs, as these parts play a crucial role in engine performance. If the check engine light is illuminated, use an OBD-II scanner to retrieve any diagnostic trouble codes, which can guide you to more specific issues. By following this structured approach, you can effectively identify and resolve the underlying causes of rough idle in your ML350, ensuring a smoother driving experience.

What Are the Common Causes of Rough Idle in a Mercedes-Benz ML350?

When dealing with a rough idle in your Mercedes-Benz ML350, it's crucial to understand the common problems that could be causing this issue. One of the primary culprits is a vacuum leak, which can disrupt the air-fuel mixture and lead to an unstable idle. Inspecting hoses and connections for any signs of wear or damage can help identify this problem. Additionally, worn or faulty spark plugs can significantly affect engine performance, so checking their condition and replacing them if necessary is a good step. Another potential issue is the ignition coil; if it's malfunctioning, it can lead to misfires and a rough idle. By systematically examining these components, you can diagnose and address the root causes of a rough idle, ensuring your ML350 runs smoothly and efficiently.

Why is a Rough Idle in a Mercedes-Benz ML350 a Cause for Concern?

A rough idle in your Mercedes-Benz ML350 should not be taken lightly, as it can signal serious underlying issues that require immediate attention. Ignoring this symptom may lead to engine misfiring, which can disrupt the delicate balance of air and fuel intake, ultimately resulting in improper cylinder compression. This not only affects your vehicle's performance but can also escalate into more severe problems, such as damage to the engine components. Furthermore, a rough idle can indicate issues like vacuum leaks or faulty spark plugs, which, if left unaddressed, could compromise the overall functionality and longevity of your vehicle. Therefore, it is crucial to diagnose and resolve these issues promptly to avoid costly repairs and ensure the safe operation of your ML350. Taking action at the first sign of a rough idle can save you from more significant headaches down the road.

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Mercedes-Benz ML350 Rough Idle Causes & Repairs | RepairPal