Fix a Car that Idles Poorly

How to Fix a Car that Idles Poorly: Simple Solutions to a Common Problem

Poor or rough idling is one of the most common problems that you can experience in your engine. This idling is an important concern because it will be indicative of the overall health condition of the vehicle. If it idles poorly, this means that there is a problem, and it should be resolved before it gets worse.

Whether your car is idling too high or too low, these can be indications of a problem. That being said, if you would like to learn how to fix a car that idles poorly, I get you covered in the rest of this post. The most challenging is perhaps the diagnosis since there can be multiple problems. Once the source is identified, it will be easier for you to proceed with the necessary repair.

What You Will Need to Follow this Tutorial

As it will be discussed later on, there are different approaches on how to resolve the problem, depending on its cause. In these steps, the following are the materials that you have to prepare:

  • Vacuum hose
  • Sealant
  • Diagnostic scanning tool
  • Ratchet
  • Spray throttle cleaner
  • Cotton swabs

Quick Guide on How to Fix a Car that Idles Poorly

In this section, I will let you know some of the most common causes of poor idling and the best approaches to solve the issue.

Fix a Car that Idles Poorly


Leaking of Broken Vacuum

If you can hear a whistle when you start the engine, chances are, you have a problem with the vacuum line. Over time, the vacuum can be prone to wear and can experience physical damage, such as cracks and leaks. When it is damaged, the car won’t be able to draw as much energy from the fuel, and hence, the performance is compromised. This is what leads to poor idling.

The simplest thing that you can do is to inspect the vacuum. In most cases, it may not be connected or it is loose. With this, a simple adjustment can already address the problem. If there are leaks, you might need to have it replaced or cover the leaks, if they can still be saved.

Idle Air Control Valve

In some cases, the problem can be more serious. If the vacuum hose seems to be working perfectly fine but the poor idling is still a persistent problem, one of the problems could be the idle air control valve (IAC). Along with the computer, its main function is to regulate the amount of air that goes in and out.

There are many ways by which it will be possible to see if the IAC is indeed the problem. One way to do this is to use a diagnostic tool. An OBD I or OBD II scanner will be helpful, depending on what year your vehicle has been made. Connect the scanner to your dash and see if the error codes would refer to possible IAC problems. These codes can be different depending on the brand of your vehicle.

Take it off and see if there is carbon buildup. If there is, this can possibly be the problem why there is poor idling. It prevents the valve from opening and moving. This could lead to letting too much air in or not letting sufficient air pass through the valve.

If the IAC is the problem, you will have two choices – replacement or cleaning. A replacement is needed if the problem has already escalated. The good news is that, in most instances, cleaning the valve and getting rid of the carbon buildup will already prove to be sufficient.

First, take off the IAC from its position. To do this, you will need to use a ratchet. Loosen the screws and make sure to keep them in a safe place, as you will have to return them later on. Inspect the IAC and see if there is gunk. If there is, the next step would be to have it removed.

To get rid of the carbon deposit, you will need to use a throttle body cleaner. Spray the cleaner and use cotton swabs to take off the gunk. Spray the cleaner again and let it soak for at least five minutes. Drain any remaining fluid and re-assemble.

Before doing this step, however, you have to check your car’s manual to be sure that you can use a throttle cleaner.

Watch the short video below for a visual guide of the things that have been mentioned above:

Pro Tips

Aside from those that have been mentioned above, you also have to keep in mind these things:

  • Your idle speed setting can also be a problem. This is one thing that is best done by a professional who knows better. Seek help from a trained mechanic.
  • Another part that might require a replacement would be the spark plug. They produce the spark that is necessary for the burning of fuel. If they are not working properly, chances are, you will end up suffering from poor idling.
  • You have to check the electrical components and see to it that they are working properly so that our car will not idle poorly. Aside from the spark plugs, you also have to inspect the coils and plug wires, among others.
  • Regular replacement of the filters will also help to prevent poor idling. Ideally, you have to install new filters right after every tune-up. It prevents dirt and debris from entering the engine, hence, providing you with the assurance that the latter will deliver optimal performance all the time.
  • Before you open the hood and inspect the engine, make sure that the car is turned off. Allow a few minutes for the system to cool down before you work. To be safe, it is best if you wear gloves so that your hands will be protected.


After reading this guide, I hope that you have been enlightened on how to fix a car that idles poorly. There are many possible causes, but the main problem could be with the IAC. In most cases, you can have it cleaned to get rid of the carbon build-up. If such can no longer be done, you will be required to have a replacement.

A poorly idling car needs your attention. If it is not addressed at the soonest possible time, this can compromise the functionality of the engine and the performance of your vehicle. That being said, it is necessary to act with urgency and execute an effective solution once you notice poor idling.

Have you experienced a car that is idling poorly? How did you address the problem? Let us know in the comment section below.