2009 Mercedes-Benz GL550 Has Rough Idle

Resolve Rough Idle in 2009 Mercedes-Benz GL550 for a Smoother Ride

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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 2009 Mercedes-Benz GL550 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 2009 Mercedes-Benz GL550 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 2009 Mercedes-Benz GL550?

When addressing a rough idle in your 2009 Mercedes-Benz GL550, start by checking for vacuum leaks, as these can significantly disrupt the air-fuel mixture and lead to performance issues. Carefully inspect all vacuum lines and hoses for any signs of cracks or disconnections. Next, consider the mass airflow sensor (MAF); a simple test involves unplugging the MAF and taking the vehicle for a short drive to see if the idle improves, which can indicate a malfunctioning sensor. Additionally, examine the cam sensors and solenoids by removing their connectors to check for oil contamination, as this can impair their function and contribute to rough idling. By systematically following these diagnostic steps, you can effectively identify and address the underlying causes of the rough idle, potentially saving time and repair costs.

What are the common problems that could cause a rough idle in a 2009 Mercedes-Benz GL550?

When diagnosing a rough idle in a 2009 Mercedes-Benz GL550, it's essential to consider several common problems that could be affecting the vehicle's performance. One of the primary culprits is a dirty or faulty mass airflow sensor, which can disrupt the delicate balance of the air-fuel mixture, leading to an unstable idle. Additionally, vacuum leaks can create an improper air-fuel ratio, further exacerbating the rough idle issue. Worn-out spark plugs or malfunctioning ignition coils are also significant factors, as they can cause engine misfires that manifest as a rough idle. Another potential issue is a clogged fuel filter, which restricts fuel flow and can hinder 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 negatively impact air intake. By systematically checking these components, DIY enthusiasts can effectively identify and resolve the underlying causes of a rough idle in their GL550.

How urgent is it to address the rough idle in a 2009 Mercedes-Benz GL550?

Addressing a rough idle in your 2009 Mercedes-Benz GL550 should be a priority, as it can signal various underlying issues that, if left unresolved, may lead to significant engine damage or safety concerns. A rough idle often points to problems with critical components such as vacuum leaks, spark plugs, or the fuel system, which can deteriorate further over time. Ignoring these symptoms not only risks worsening the condition of your vehicle but can also compromise its drivability, making for an uncomfortable and potentially unsafe driving experience. By tackling the rough idle promptly, you can prevent more extensive repairs down the line, ensuring that your vehicle remains reliable and efficient. Therefore, if you notice any irregularities in your engine's performance, it is advisable to investigate and address the issue as soon as possible to maintain the health and longevity of your GL550.

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