1999 Toyota Tacoma Has Rough Idle

Diagnosing Causes of Rough Idle in Your 1999 Toyota Tacoma and How to Restore Smooth Performance

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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 1999 Toyota Tacoma 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 1999 Toyota Tacoma 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 1999 Toyota Tacoma?

To effectively diagnose a rough idle in your 1999 Toyota Tacoma, start with a systematic approach that prioritizes simpler checks before delving into more complex diagnostics. Begin by inspecting for vacuum leaks, as these can significantly impact engine performance. Next, examine the condition of the spark plugs; worn or fouled plugs can lead to misfires and rough idling. A clean air filter is also crucial, so ensure it is free from dirt and debris that could disrupt the air-fuel mixture. Following this, test the fuel system, including fuel pressure and injectors, to confirm they are operating correctly. Utilizing an OBD-II scanner can help identify any error codes related to sensors or components that may be malfunctioning. Additionally, check the Idle Air Control (IAC) valve for any buildup that could hinder its function, and clean the throttle body to promote smooth airflow. Lastly, don’t overlook the coolant level, as low coolant can lead to overheating and exacerbate idle issues. By following this diagnostic approach, you can efficiently pinpoint and resolve the factors contributing to a rough idle in your Tacoma.

What are the common causes of a rough idle in a 1999 Toyota Tacoma?

When dealing with a rough idle in a 1999 Toyota Tacoma, it's crucial to understand the common problems that may be at play. One of the primary culprits is a dirty or clogged air filter, which can significantly restrict airflow to the engine, resulting in an uneven idle. Additionally, faulty spark plugs are notorious for causing misfires; if they are worn out, they can lead to a rough running engine. Another potential issue is vacuum leaks, which can disrupt the delicate air-fuel mixture necessary for smooth operation. Problems within the fuel system, such as a clogged fuel filter or malfunctioning fuel injectors, can also hinder engine performance and contribute to rough idling. Furthermore, ignition system problems, including a malfunctioning ignition coil or distributor, can exacerbate the situation. Lastly, a dirty or malfunctioning throttle body can impede proper air intake, further complicating the idle issue. By identifying and addressing these common problems, DIYers can effectively troubleshoot and resolve rough idle issues, ensuring their Tacoma runs smoothly and efficiently.

How urgent is it to address the rough idle in my 1999 Toyota Tacoma?

Addressing a rough idle in your 1999 Toyota Tacoma is not just a matter of comfort; it is crucial for the vehicle's overall performance and longevity. Ignoring this symptom can lead to a cascade of problems, including decreased fuel efficiency and engine misfires, which can further exacerbate the situation and result in costly repairs. A rough idle often indicates underlying issues such as faulty spark plugs, fuel system malfunctions, or air intake problems that, if left unattended, could escalate into more serious engine damage. Moreover, the longer you wait to address these symptoms, the more likely you are to face significant safety risks while driving. Therefore, it is essential to prioritize this issue and take the necessary steps to diagnose and resolve the rough idle promptly, ensuring your Tacoma remains reliable and efficient on the road.

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