Lexus NX350h Has Rough Idle

Troubleshooting Causes of Rough Idle in Your Lexus NX350h and Solutions for a Smoother Ride

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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 Lexus NX350h 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 Lexus NX350h 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.

Brake caliper failure occurs in two different ways, and they create different symptoms.

The caliper can become stuck, in which case it won't release the brake pads. The seized caliper will cause the vehicle to brake constantly on one side, forcing the car to move toward that side. This pulling will be accompanied by a strong odor from one wheel.

Another way calipers fail is by leaking. If the caliper leaks, the brake pedal will feel too easy to push, and will sink all the way to the floor when held. Braking will become less effective the longer this goes on. There may also be brake fluid leaking onto the wheel.

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.

Brake rotors are mainly maintenance free, but when they have been subjected to abnormally hard use, the heat they absorb can cause the metal to turn blue, and cracking to occur. When this occurs, customers often specify they have lost braking power, or the vehicle's brakes are making noise. There may be no symptoms at all related to changing the brake rotors, since it is recommended to change brake rotors on most modern vehicles when performing a standard brake service.

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.

Troubleshooting Rough Idle in a Lexus NX350h

When faced with a rough idle in your Lexus NX350h, begin your diagnostic approach by checking for simple issues that can often be the root cause. Start by inspecting the vacuum lines for any signs of leaks, as even a small crack can disrupt the air-fuel mixture and lead to an unstable idle. Next, examine the spark plugs and ignition coils; worn or faulty components can cause misfires, contributing to rough idling. If these initial checks do not resolve the issue, consider inspecting the fuel system, including the fuel injectors, for clogs or malfunctions that may affect engine performance. It’s also wise to verify that the idle speed is set correctly, ideally between 600 to 1,000 RPMs, as incorrect settings can exacerbate idle problems. If these steps do not yield results, it may be time to consult a professional for a more thorough evaluation, as they can diagnose more complex issues that may not be immediately apparent. Regular maintenance and timely inspections are essential to ensure your Lexus NX350h runs smoothly, preventing minor issues from escalating into major repairs.

What Are the Common Causes of Rough Idle in a Lexus NX350h?

When dealing with a rough idle in your Lexus NX350h, it's essential to consider several common problems that could be affecting your vehicle's performance. One of the primary suspects is a vacuum leak, which can disrupt the air-fuel mixture and lead to an unstable idle. Additionally, worn or faulty spark plugs can cause misfires, resulting in a rough idle as well. The ignition coil is another critical component; if it malfunctions, it can prevent the engine from firing correctly, leading to similar symptoms. A dirty or malfunctioning mass airflow sensor (MAF) can also be a significant factor, as it plays a crucial role in measuring the air entering the engine and ensuring the right fuel mixture. Furthermore, issues within the fuel system, such as clogged fuel injectors or a failing fuel pump, can contribute to poor engine performance and rough idling. Lastly, don't overlook the ignition control module, plug wires, and any defective sensors, as these can also lead to irregular engine behavior. By understanding these potential causes, you can effectively diagnose and address the rough idle issue in your Lexus NX350h, making your DIY repair efforts more successful.

Why is a Rough Idle in a Lexus NX350h a Cause for Urgent Attention?

A rough idle in your Lexus NX350h should never be overlooked, as it can signal serious underlying problems that require immediate attention. Common culprits like vacuum leaks, faulty spark plugs, or malfunctioning ignition coils can disrupt engine performance, leading to increased emissions and reduced fuel efficiency. If left unaddressed, these issues can escalate, potentially resulting in engine stalling or more extensive damage that could incur costly repairs. Moreover, a failing ignition coil often triggers the check engine light, serving as a clear warning that something is amiss. By diagnosing and resolving a rough idle promptly, you not only safeguard your vehicle's performance but also enhance its longevity. Regular maintenance and timely intervention are key to ensuring your Lexus NX350h runs smoothly, making it essential for DIY enthusiasts to stay vigilant and proactive in addressing any signs of rough idling.

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