2012 Mercedes-Benz GL350 Has Rough Idle

Diagnosing Causes of Rough Idle in Your 2012 Mercedes-Benz GL350 and Solutions 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 2012 Mercedes-Benz GL350 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 2012 Mercedes-Benz GL350 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 2012 Mercedes-Benz GL350?

When faced with a rough idle in your 2012 Mercedes-Benz GLK350, start by checking for a vacuum leak, as this is a common culprit that can significantly affect engine performance. Next, inspect the spark plugs for any signs of wear or damage, since faulty spark plugs can lead to misfires and an uneven idle. Following this, examine the ignition coil to ensure it is functioning properly, as issues here can also contribute to rough idling. Conducting a diagnostic scan is essential to identify any misfiring cylinders, which will help you narrow down the problem. Additionally, consider unplugging the Mass Air Flow (MAF) sensor and taking the vehicle for a test drive; if the idle improves, this sensor may need replacement. Monitoring the O2 sensor readings through the OBD1 port can provide valuable insights into the fuel trim levels, indicating potential issues. Lastly, increasing the idle RPM to 1500 and observing any changes in misfire counts can further clarify whether misfires are a significant factor in the rough idle. By systematically following these steps, you can effectively diagnose and address the rough idle issue in your vehicle.

What are the common causes of a rough idle in a 2012 Mercedes-Benz GL350?

When dealing with a rough idle in your 2012 Mercedes-Benz GL350, it's crucial to understand the common problems that could be at play. One of the primary culprits is dirty or faulty spark plugs, which can hinder proper ignition and lead to an uneven idle. Additionally, a clogged fuel filter may restrict fuel flow, further exacerbating the issue. It's also important to check for vacuum leaks, as these can disrupt the air-fuel mixture essential for smooth engine operation. Another potential problem is a malfunctioning mass airflow sensor (MAF), which can provide incorrect airflow readings, negatively impacting idle quality. The idle air control valve (IAC) is another component to inspect, as issues here can cause irregular idle speeds. Lastly, a faulty oxygen sensor can throw off the air-fuel mixture, contributing to a rough idle. By systematically checking these components, you can effectively diagnose and address the rough idle, ensuring your GL350 runs smoothly.

How urgent is it to address the rough idle in my 2012 Mercedes-Benz GL350?

Addressing a rough idle in your 2012 Mercedes-Benz GL350 is not just a matter of comfort; it is essential for the safety and longevity of your vehicle. A rough idle can indicate serious underlying problems such as faulty spark plugs, fuel system malfunctions, or engine misfires, which, if left unattended, can escalate into more significant issues. Ignoring these symptoms may lead to decreased fuel efficiency, increased emissions, and even engine damage, which can result in costly repairs. Moreover, a rough idle can compromise your vehicle's performance and safety, making it crucial to diagnose and resolve the issue promptly. Regular maintenance and timely repairs not only enhance your driving experience but also prevent potential hazards on the road. Therefore, if you notice your GL350 idling roughly, it is advisable to investigate the cause and seek professional assistance to ensure your vehicle remains in optimal condition.

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