2018 Ford Fiesta Has Rough Idle

Diagnosing Causes of Rough Idle in Your 2018 Ford Fiesta and How to Restore Smooth Performance

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Reviewed by
Aisha
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 2018 Ford Fiesta 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 2018 Ford Fiesta 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 2018 Ford Fiesta?

When faced with a rough idle in your 2018 Ford Fiesta, it's essential to start with a systematic diagnostic approach. Begin by checking the spark plugs, as worn or faulty plugs can significantly impact engine performance. Next, inspect the air filter; a dirty or clogged filter can restrict airflow, leading to an uneven idle. Following this, examine the fuel system, including the fuel filter and injectors, to ensure that fuel delivery is optimal. Utilizing an OBD-II scanner to check for error codes can provide insights into any underlying issues that may not be immediately visible. Additionally, look for vacuum leaks in hoses and connections, as these can disrupt engine performance. Finally, cleaning the throttle body can help restore proper airflow and function. By methodically addressing these areas, you can effectively diagnose and potentially resolve the rough idle issue in your vehicle.

What are the common causes of a rough idle in a 2018 Ford Fiesta?

When experiencing a rough idle in your 2018 Ford Fiesta, it's essential to consider several common problems that could be at play. One of the first areas to inspect is the air filter; a dirty or clogged filter can significantly restrict airflow to the engine, leading to an unstable idle. Additionally, spark plugs should be checked for wear or fouling, as these can cause misfires that disrupt the engine's smooth operation. The mass airflow sensor is another critical component; if it's malfunctioning, it can throw off the air-fuel mixture, resulting in a rough idle. Fuel injectors also play a vital role in maintaining engine performance, so ensure they are free from clogs or leaks that could hinder fuel delivery. Don't overlook the possibility of vacuum leaks in the intake system, which can create air imbalances and lead to an uneven idle. Lastly, faulty ignition coils can contribute to rough idling by causing inconsistent engine operation. By systematically addressing these issues, you can enhance the idle quality of your Fiesta and ensure a smoother driving experience.

How urgent is it to address the rough idle in my 2018 Ford Fiesta?

Addressing a rough idle in your 2018 Ford Fiesta is not just a matter of comfort; it is crucial for the overall health of your vehicle. A rough idle can indicate serious underlying problems, such as issues with the fuel system, ignition components, or even engine wear. If left unattended, these problems can escalate, leading to more significant damage and costly repairs. Moreover, a rough idle often results in decreased fuel efficiency, which can strain your budget over time. By prioritizing the resolution of this issue, you not only enhance your driving experience but also safeguard your engine's longevity and performance. Therefore, it is essential to take immediate action to diagnose and fix the rough idle, ensuring your Ford Fiesta remains reliable and efficient on the road.

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