2009 Lexus IS350 Has Rough Idle

Troubleshooting Causes of Rough Idle in Your 2009 Lexus IS350 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 2009 Lexus IS350 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 2009 Lexus IS350 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.

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 2009 Lexus IS350?

When diagnosing a rough idle in a 2009 Lexus IS350, it's essential to adopt a systematic approach that prioritizes simpler checks before delving into more complex diagnostics. Start by using an OBD-II scanner to identify any error codes, as these can pinpoint specific issues affecting engine performance. Next, inspect the spark plugs for wear or fouling, as these components play a crucial role in engine combustion. A clean air filter is also vital; ensure it is free from dirt and debris to maintain proper airflow. Additionally, examine the vacuum hoses for any signs of damage or leaks, as these can significantly impact engine idle quality. The fuel system should not be overlooked; check the fuel filter and injectors for clogs or dirt that could disrupt fuel delivery. Finally, assess the throttle body for cleanliness and functionality, as a dirty throttle body can lead to irregular idling. By following this structured diagnostic approach, you can effectively identify and resolve the underlying causes of a rough idle in your vehicle.

What are the common problems that could cause a rough idle in a 2009 Lexus IS350?

When diagnosing a rough idle in a 2009 Lexus IS350, it's essential to consider several common problems that could be affecting the vehicle's performance. One of the primary culprits is a dirty or faulty mass airflow sensor, which can disrupt the delicate balance of the air-fuel mixture necessary for smooth engine operation. Additionally, vacuum leaks can lead to an improper air-fuel ratio, exacerbating idle issues. Worn-out spark plugs or malfunctioning ignition coils may also cause misfires, contributing to a rough idle experience. Another factor to investigate is the fuel filter; if it becomes clogged, it can restrict fuel flow, further impacting engine performance. The idle air control valve is another critical component that, if malfunctioning, can disrupt the engine's idle speed. Lastly, issues with the throttle body, such as carbon buildup, can hinder airflow and lead to rough idling. By systematically checking these components, DIY enthusiasts can effectively diagnose and potentially resolve the rough idle issue in their Lexus IS350.

How urgent is it to address the rough idle in my 2009 Lexus IS350?

Addressing a rough idle in your 2009 Lexus IS350 is not just a matter of comfort; it is crucial for the vehicle's overall performance and safety. A rough idle can indicate serious underlying issues, such as faulty spark plugs, fuel system malfunctions, or air intake problems, which, if left unattended, can escalate into more significant engine damage. Ignoring these symptoms may lead to decreased fuel efficiency, increased emissions, and even engine stalling, posing safety risks on the road. Moreover, the longer you wait to address the problem, the more costly the repairs may become, as neglect can lead to further deterioration of engine components. Regular maintenance and prompt repairs are essential to ensure your vehicle runs smoothly and efficiently, ultimately prolonging its lifespan. Therefore, it is highly advisable to consult a professional mechanic at the first sign of a rough idle to prevent complications and maintain the reliability of your Lexus IS350.

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