2009 Mercury Mariner Has Rough Idle

Common Causes of Rough Idling in Your 2009 Mercury Mariner and How to Resolve Them

Find Repair Location
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 2009 Mercury Mariner 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 2009 Mercury Mariner 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.

Customers with drum brake systems often specify they have lost braking power, or that the vehicle's brakes are making noise. This is because brake drums do not dissipate heat very well, so the heat from hard braking will cause stress fractures. These fractures make can make noise on the brake shoes as the drum revolves around the shoes. Lastly, the brake shoes may not be problematic, but may cause a grinding noise while stopping. This would indicate the shoes have no braking material left, and the brake shoes must be changed before the vehicle can be safely driven.

Learn more about brake shoe symptoms

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 Mercury Mariner?

When addressing a rough idle in your 2009 Mercury Mariner, start by checking for common issues that could be affecting engine performance. Begin with a visual inspection of the throttle body, as dirt or buildup can disrupt airflow and lead to idling problems. If the check engine light is illuminated, retrieving trouble codes can provide valuable insights into specific issues. Next, ensure that the engine is receiving the right mix of air, fuel, and spark; this involves checking the air intake system, fuel injectors, and spark plugs for any signs of wear or malfunction. Additionally, inspect the throttle position sensor (TPS) to confirm it is functioning correctly, as an improperly calibrated TPS can significantly impact idle quality. By systematically addressing these areas, you can effectively diagnose and potentially resolve the rough idle issue, making your DIY repair process more efficient and successful.

What are the common causes of a rough idle in a 2009 Mercury Mariner?

When diagnosing a rough idle in a 2009 Mercury Mariner, it's essential to consider several common problems that could be affecting the vehicle's performance. One of the primary culprits is a vacuum leak, which can significantly disrupt the air-to-fuel ratio necessary for optimal combustion, leading to an unstable idle. Additionally, issues with the spark plugs, such as fouling or incorrect gapping, can cause misfires, particularly noticeable at low RPMs. The ignition coil is another critical component; if it's malfunctioning, it may not provide the necessary spark for ignition, further contributing to rough idling. Furthermore, a misfire or a bad motor mount can result in noticeable shaking when the vehicle is idling, indicating a need for inspection. Lastly, a faulty throttle body can lead to erratic engine behavior, often accompanied by symptoms like dirt buildup, the illumination of the check engine light, and an unstable idle. Addressing these issues through careful diagnosis and repair can help restore smooth operation to your Mercury Mariner.

You’ve got options with RepairPal

Whether you need a more accurate auto repair estimate or help finding a reputable shop in your area, we’ve got you covered.