2012 Mercedes-Benz R350 Has Rough Idle

Resolve Rough Idle in Your 2012 Mercedes-Benz R350 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 2012 Mercedes-Benz R350 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 R350 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 potential causes and diagnostic steps for a rough idle in a 2012 Mercedes-Benz R350?

When tackling a rough idle in your 2012 Mercedes-Benz R350, it's essential to adopt a systematic diagnostic approach. Start by checking for engine misfires, as these can significantly disrupt idle quality. Utilize a diagnostic tool to scan for any trouble codes that may indicate misfiring cylinders. Next, inspect the camshaft adjusters, as issues here can lead to rattling noises and contribute to an uneven idle. Following this, test the fuel injectors, particularly when the engine is cold, to ensure they are delivering fuel efficiently. Additionally, don't overlook the possibility of vacuum leaks; inspect all vacuum lines for any signs of damage or leaks that could affect engine performance. Lastly, consider cleaning the throttle body, as a buildup of carbon can impede airflow and lead to rough idling. By methodically addressing these areas, you can effectively identify and resolve the underlying issues affecting your vehicle's idle.

What are the common causes of a rough idle in a 2012 Mercedes-Benz R350?

When diagnosing a rough idle in your 2012 Mercedes-Benz R350, it's crucial to consider several 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, clogged fuel injectors may prevent the engine from receiving the proper fuel supply, further exacerbating the roughness. Another potential issue is vacuum leaks, which can disrupt the air-fuel mixture necessary for smooth engine operation. The mass airflow sensor (MAF) also plays a vital role; if it malfunctions, it can send incorrect airflow readings to the engine control unit, negatively impacting performance. Furthermore, the idle air control valve (IAC) is essential for maintaining the correct idle speed, and any issues here can lead to instability. Lastly, a faulty oxygen sensor can cause the engine to run either too rich or too lean, affecting idle quality. Addressing these issues promptly is essential for restoring the smooth operation of your vehicle.

How urgent is it to address the rough idle in my 2012 Mercedes-Benz R350?

Addressing a rough idle in your 2012 Mercedes-Benz R350 is crucial for maintaining the vehicle's performance and longevity. 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 escalate into more severe engine damage over time. A rough idle often indicates underlying issues such as faulty spark plugs, vacuum leaks, or fuel system malfunctions, which, if left unresolved, may result in costly repairs. Moreover, neglecting these symptoms can compromise your vehicle's safety and reliability, making it essential to act promptly. Regular maintenance and timely intervention not only enhance your vehicle's performance but also help you avoid the financial burden of extensive repairs down the line. Therefore, if you notice a rough idle, it is advisable to investigate and address the issue as soon as possible to ensure your 2012 Mercedes-Benz R350 continues to operate smoothly and efficiently.

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