2008 Smart Fortwo Has Rough Idle

Troubleshooting Causes of Rough Idle in Your 2008 Smart Fortwo and How to Resolve Them

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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 2008 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 2008 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 a rough idle in a 2008 Smart Fortwo?

To effectively diagnose a rough idle in your 2008 Smart Fortwo, start with the simplest solutions before moving on to more intricate assessments. Begin by using an OBD-II scanner to check for any fault codes, as these can quickly point you to underlying issues. Next, inspect the spark plugs; worn or fouled plugs can cause misfires, so replacing them may resolve the problem. Don’t overlook the air filter; a clean filter is essential for optimal airflow, so replace it if it appears dirty. After that, examine the vacuum lines for any leaks, as these can disrupt the air-fuel mixture and lead to rough idling. Moving on, check the fuel system, including the fuel filter and injectors, as clogs or malfunctions here can significantly impact performance. The idle control valve is another critical component; ensure it’s functioning correctly, as a faulty valve can cause erratic idling. Additionally, inspect the throttle body for carbon buildup, which can hinder its operation, and clean it if necessary. Finally, assess the engine mounts; if they are worn or damaged, they can contribute to vibrations and a rough idle. By following this structured approach, you can systematically identify and address the issues causing the rough idle, enhancing your vehicle's performance and drivability.

What are the common problems that could cause a rough idle in a 2008 Smart Fortwo?

When diagnosing a rough idle in a 2008 Smart Fortwo, it's essential to consider several common problems that could be affecting your vehicle's 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. Another potential issue is vacuum leaks; these can disrupt the air-fuel mixture, resulting in poor engine performance. Fuel system problems, such as a clogged fuel filter or a malfunctioning fuel pump, can hinder fuel delivery, further exacerbating idle issues. Furthermore, a faulty mass airflow sensor may provide incorrect readings, affecting the air-fuel mixture and leading to rough idling. Lastly, a dirty throttle body can restrict airflow and disrupt the engine's idle speed. By addressing these common issues through regular maintenance and timely repairs, you can effectively resolve rough idle problems and ensure your Smart Fortwo runs smoothly.

How urgent is it to address the rough idle in a 2008 Smart Fortwo?

Addressing a rough idle in a 2008 Smart Fortwo is crucial for maintaining the vehicle's overall health and performance. Ignoring this symptom can lead to more severe engine problems, which may result in costly repairs down the line. A rough idle often indicates underlying issues within the engine or fuel system, such as a malfunctioning spark plug, clogged fuel injectors, or vacuum leaks. These problems, if left unaddressed, can escalate, potentially compromising the vehicle's safety and reliability. For DIY enthusiasts, it is essential to recognize that while some minor adjustments can be made at home, a professional diagnosis is often necessary to pinpoint the exact cause of the rough idle. Taking prompt action not only helps in preserving the engine's integrity but also ensures a smoother driving experience, making it imperative to tackle this issue as soon as it arises.

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2008 Smart Fortwo Rough Idle Diagnosis & Solutions