2012 Mercedes-Benz C250 Has Rough Idle

Diagnosing Causes of Rough Idle in Your 2012 Mercedes-Benz C250 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 C250 has rough idle are a vacuum leak, an issue with the spark plugs, or a problem with the ignition coil.
  • Spark Plugs: A worn or fouled spark plug can cause misfires, rough idling, and decreased fuel efficiency due to incomplete combustion.
  • 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 C250 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 C250?

When addressing a rough idle in your 2012 Mercedes-Benz C250, start by checking for vacuum leaks, as these are often the primary culprits behind idle issues. Inspecting the vacuum hoses and intake manifold for any signs of wear or disconnection can reveal simple fixes that may resolve the problem. Next, examine the spark plugs; worn or fouled plugs can disrupt the combustion process, leading to an uneven idle. If the spark plugs appear to be in good condition, turn your attention to the ignition coil, as a malfunctioning coil can also cause misfires and rough idling. To gain deeper insights, utilize a scan tool to monitor live engine data while the engine is running; this can help you identify specific misfires or irregularities in engine performance. Finally, performing an OBD-II scan will allow you to check for any stored trouble codes that could indicate underlying issues requiring further attention. By systematically following these diagnostic steps, you can effectively identify and address the root causes of a rough idle in your vehicle.

What are the common causes of a rough idle in a 2012 Mercedes-Benz C250?

When experiencing a rough idle in a 2012 Mercedes-Benz C250, it's crucial to consider several common problems that could be at play. One of the most frequent culprits is a vacuum leak, which can disrupt the air-fuel mixture and lead to an unstable engine performance. Additionally, issues with the spark plugs can cause misfires, resulting in a rough-running engine. If the spark plugs are worn or damaged, they may not ignite the fuel properly, leading to stumbling and poor idle. Another potential issue is a malfunctioning ignition coil, which is responsible for delivering the spark needed for combustion. If the ignition coil is failing, it can lead to inconsistent firing of the engine cylinders, further contributing to a rough idle. Addressing these issues promptly is essential for maintaining the vehicle's performance and ensuring a smooth driving experience.

How urgent is it to address the rough idle in my 2012 Mercedes-Benz C250?

Addressing a rough idle in your 2012 Mercedes-Benz C250 is crucial for maintaining the vehicle's performance and safety. A rough idle can signal underlying engine problems that, if ignored, may escalate into more severe issues, leading to costly repairs and decreased fuel efficiency. Moreover, neglecting this symptom could compromise critical systems, posing safety risks while driving. By diagnosing and resolving the rough idle early, you not only enhance your vehicle's reliability but also prevent further damage that could arise from prolonged neglect. Regular maintenance and timely repairs are essential for the longevity of your car, making it imperative to take action as soon as you notice any irregularities in engine performance. Prioritizing this issue will ensure that your Mercedes-Benz C250 continues to operate smoothly and efficiently.

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2012 Mercedes-Benz C250 Rough Idle Causes & Repairs