2018 Ford Focus Has Rough Idle

Common Causes of Rough Idling in Your 2018 Ford Focus and How to Resolve Them

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Reviewed by
Bo Fader
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 Focus 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 Focus 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 steps to diagnose a rough idle in a 2018 Ford Focus?

To effectively diagnose a rough idle in your 2018 Ford Focus, start with the simplest solutions before progressing to more intricate assessments. Begin by using an OBD-II scanner to check for any error codes, as these can quickly point you to underlying issues. Next, inspect the spark plugs for wear or damage, since faulty plugs can lead to misfires that contribute to a rough idle. Don’t overlook the air filter; a clogged filter can restrict airflow, so ensure it’s clean and functioning properly. Additionally, examine the vacuum hoses for any cracks or disconnections, as leaks can significantly impact engine performance. Moving on, take a look at the fuel system, including the fuel filter and injectors, since blockages here can disrupt fuel delivery. Testing the mass airflow sensor is also crucial, as a malfunction can lead to an incorrect air/fuel mixture. Finally, inspect the throttle body for any carbon buildup or dirt that may hinder its operation. By following this structured approach, you can effectively identify and address the causes of a rough idle in your vehicle.

What are the common problems that could cause a rough idle in a 2018 Ford Focus?

When dealing with a rough idle in your 2018 Ford Focus, it's essential to consider several common problems that could be at play. One of the primary culprits is a dirty or faulty mass airflow sensor, which can disrupt the delicate balance of air and fuel entering the engine. Additionally, vacuum leaks in the intake system can lead to an improper air-fuel mixture, exacerbating the rough idle. Worn-out or faulty spark plugs are another frequent issue, as they can cause misfires that affect engine performance. A clogged fuel filter may also restrict fuel flow, resulting in an uneven idle. Furthermore, problems with the idle air control valve can disrupt the engine's idle speed, while a malfunctioning oxygen sensor can cause the engine to run either too rich or too lean, both of which contribute to rough idling. By identifying and addressing these issues through regular maintenance and timely repairs, you can significantly improve your vehicle's performance and restore a smooth idle.

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

Addressing a rough idle in your 2018 Ford Focus is not just a matter of comfort; it is crucial for the overall health of your vehicle. A rough idle can signal serious underlying problems, such as engine misfires or issues with fuel delivery, which, if left unattended, can escalate into more significant and costly repairs. Moreover, a rough idle often leads to decreased fuel efficiency, meaning you could be spending more on gas while your vehicle's performance suffers. Ignoring these symptoms can also result in further damage to the engine, potentially compromising its longevity and reliability. Therefore, it is essential to prioritize this issue and seek timely repairs to maintain optimal performance and avoid more severe consequences down the line. Taking action now can save you from future headaches and expenses, ensuring your Ford Focus runs smoothly for years to come.

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