2021 Mercedes-Benz GLE350 Has Rough Idle

Diagnosing the Causes of Rough Idle in Your 2021 Mercedes-Benz GLE350 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 2021 Mercedes-Benz GLE350 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 2021 Mercedes-Benz GLE350 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.

Brake caliper failure occurs in two different ways, and they create different symptoms.

The caliper can become stuck, in which case it won't release the brake pads. The seized caliper will cause the vehicle to brake constantly on one side, forcing the car to move toward that side. This pulling will be accompanied by a strong odor from one wheel.

Another way calipers fail is by leaking. If the caliper leaks, the brake pedal will feel too easy to push, and will sink all the way to the floor when held. Braking will become less effective the longer this goes on. There may also be brake fluid leaking onto the wheel.

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.

Brake rotors are mainly maintenance free, but when they have been subjected to abnormally hard use, the heat they absorb can cause the metal to turn blue, and cracking to occur. When this occurs, customers often specify they have lost braking power, or the vehicle's brakes are making noise. There may be no symptoms at all related to changing the brake rotors, since it is recommended to change brake rotors on most modern vehicles when performing a standard brake service.

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 2021 Mercedes-Benz GLE350?

To effectively diagnose a rough idle in your 2021 Mercedes-Benz GLE350, start with a systematic approach that prioritizes simpler checks before delving into more complex diagnostics. Begin by using an OBD-II scanner to identify any error codes, as these can pinpoint specific issues affecting engine performance. Next, inspect the spark plugs for wear or fouling, as these components play a crucial role in engine combustion. A clean air filter is essential for optimal airflow, so check its condition and replace it if it appears dirty or clogged. Moving on, examine the fuel system, including the fuel filter and injectors, to ensure they are functioning correctly, as any malfunction here can contribute to a rough idle. Don’t overlook the vacuum hoses; inspect them for leaks or damage, as these can significantly impact engine performance. Additionally, cleaning the throttle body can help maintain proper airflow and improve the air-fuel mixture. Finally, consider performing a smoke test to detect any vacuum leaks in the intake system, which can further disrupt the engine's performance. By following this structured diagnostic approach, you can effectively identify and address the underlying causes of a rough idle in your vehicle.

What are the common problems that could cause a rough idle in a 2021 Mercedes-Benz GLE350?

When dealing with a rough idle in your 2021 Mercedes-Benz GLE350, 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 lead to engine misfires and an uneven idle. Additionally, vacuum leaks can disrupt the delicate air-fuel mixture, causing instability in engine performance. Another significant factor is the mass airflow sensor; if it's malfunctioning, it can throw off the air-fuel ratio, exacerbating the rough idle. A clogged fuel filter may also be a concern, as it restricts fuel flow and can lead to performance issues. Furthermore, the EGR valve plays a vital role in managing emissions, and any issues here can affect idle quality. Lastly, a faulty oxygen sensor can provide incorrect readings, further complicating the air-fuel mixture. Addressing these issues promptly not only enhances your vehicle's performance but also ensures a smoother driving experience. For DIY enthusiasts, diagnosing these problems can often be done with basic tools and a little mechanical knowledge, making it a manageable task.

How urgent is it to address the rough idle in a 2021 Mercedes-Benz GLE350?

Addressing a rough idle in your 2021 Mercedes-Benz GLE350 should be treated as a priority, especially if you're considering a DIY approach. A rough idle can be more than just an annoyance; it often signals underlying engine issues that, if left unchecked, can escalate into more severe problems. For instance, neglecting this symptom may lead to decreased fuel efficiency, increased emissions, and even potential engine damage, which can be costly to repair. Moreover, some causes of a rough idle can pose safety risks, such as compromised engine performance that affects your vehicle's handling. By taking the initiative to diagnose and resolve the issue promptly, you not only enhance your vehicle's performance but also ensure your safety on the road. Regular maintenance and timely repairs are key to prolonging the life of your GLE350, making it essential to address any irregularities in its operation as soon as they arise.

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2021 Mercedes-Benz GLE350 Rough Idle: Causes & Repairs