2017 Smart Fortwo Has Rough Idle

Diagnosing Causes of Rough Idle in Your 2017 Smart Fortwo and How to Restore Smooth Performance

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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 2017 Smart Fortwo 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 2017 Smart Fortwo 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 and fix a rough idle in a 2017 Smart Fortwo?

To effectively diagnose and fix a rough idle in your 2017 Smart Fortwo, start with the simplest solutions before moving on to more complex diagnostics. Begin by using an OBD-II scanner to check for any fault codes, as these can provide immediate insights into potential issues. Next, inspect the air filter; a clogged filter can significantly restrict airflow, leading to idle problems. If the air filter is clean, turn your attention to the spark plugs, as worn or fouled plugs can cause misfires that contribute to a rough idle. Following this, examine the fuel system for any clogs or faults, particularly in the fuel filter and injectors, as these components are crucial for proper engine function. Additionally, inspect the vacuum hoses for leaks or cracks, which can disrupt the air-fuel mixture. Cleaning the throttle body is also essential, as a buildup of dirt can hinder airflow. Finally, check the idle air control valve, as its malfunction can directly affect idle speed. By following this structured approach, you can systematically identify and resolve the underlying causes of a rough idle, ensuring your Smart Fortwo runs smoothly.

What are the common problems that could cause a rough idle in a 2017 Smart Fortwo?

When diagnosing a rough idle in a 2017 Smart Fortwo, it's essential to consider several common problems that could be affecting engine performance. One of the primary culprits is a dirty or clogged air filter, which can significantly restrict airflow to the engine, leading to an uneven idle. Additionally, faulty spark plugs are notorious for causing misfires, which can also contribute to a rough idle experience. Another potential issue is vacuum leaks; these can disrupt the air-fuel mixture, resulting in instability during idling. Fuel system problems, such as a clogged fuel filter or a malfunctioning fuel pump, can further exacerbate the situation by impacting the engine's overall performance. Moreover, a malfunctioning mass airflow sensor (MAF) can lead to incorrect air-fuel ratios, causing the engine to run either too rich or too lean, both of which can affect idle quality. Lastly, issues with the idle air control valve (IAC) can disrupt the engine's idle speed control, leading to further complications. By addressing these common issues through regular maintenance and timely repairs, you can ensure smoother engine operation and a more pleasant driving experience.

How urgent is it to address the rough idle in a 2017 Smart Fortwo?

Addressing a rough idle in your 2017 Smart Fortwo is crucial for maintaining the vehicle's performance and safety. A rough idle often indicates underlying engine problems that, if ignored, can escalate into more severe issues, leading to costly repairs and decreased fuel efficiency. The longer you wait to diagnose and fix the problem, the more likely it is that you will experience diminished performance and potential engine damage. Moreover, a rough idle can compromise your driving experience, making it less safe and reliable. Therefore, it is essential to prioritize this issue and seek a professional diagnosis and repair as soon as possible. By doing so, you not only enhance the longevity of your vehicle but also ensure a smoother and safer ride.

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