Home Diagnosis and TroubleshootingProcesses, Mechanics, and Repairs Why Is My Car Idling High – How Can I Diagnose And Fix This?

Why Is My Car Idling High – How Can I Diagnose And Fix This?

by Jordan Harris
Why Is My Car Idling High

Are you experiencing high idle and you are asking yourself why is my car idling high? Well, if that is the case and you find yourself in this situation, then you are at the right place because there will be a lot to cover on this topic and we are going to learn everything you need to know when it comes to this problem.

Having problems like these can be really difficult to deal with. Namely because it is rather difficult to tell right off the bat what is causing this issue and to diagnose this problem, you need to have a good knowledge of cars to troubleshoot the issue.

But luckily for you, this is why we are here to help you out when it comes to this problem and teach you everything that you need to know when it comes to proper troubleshooting and tackling the issue. In this article, we will share some secrets that only some of the most experienced mechanics out there know and we will help you tackle the issue.

First, we will learn what is engine idle and what is the proper idle speed of the engine, then we will cover the situations when you experience high idle. As well as the causes of why is my car idling high. Then we will move on to the diagnostics procedure and show you how to tackle the problem. So, if you want to learn more about this topic, follow along.

What Is High Engine Idle

Now before we dive into the topic of possible causes of why is my car idling high, let’s first take a look at what is high engine idle in general. I bet that there are a ton of people reading this article who have encountered this issue before and want to learn more about the basics when it comes to this topic. So, what is the engine idle?

Well, engine idle is considered the situation when the engine is not under load. So, what does this mean?

It means that the engine simply is running without any gas input except the input needed in order so the engine does not stall.

As you probably know, there is an RPM range through which an engine can be pushed. Starting from 0 RPM to 6,500 RPMs in most car engines. Some even rev up to 9,000 RPM or higher. But these are usually high-performance engines. So, what is the idle RPM?

The idle RPM is relatively low in this RPM range, usually at 800 RPM. Some engines idle at 600 but most of them are limited to 800 RPM.

So, we can say that any idling speed that is above 800 RPM is considered to be a high idle. If you don’t give any gas input, the engine should not surpass this limit under any circumstance. So, why is my car idling high? We will get to that in a moment, let’s first take a look and learn is if idling bad for your car.

Is Idling High Bad For My Car

Another question that we want to answer before we dive into the topic of why is my car idling high is the question, is idling bad for your car? Is that the case or not?

Actually no, engine idling will not damage your engine at all. Just imagine how many police cars are out there that are idling constantly for a whole day in some cases. And there is nothing wrong with them.

So, if you leave your car idle for an hour or a few hours, it just doesn’t matter. It won’t change anything for your engine. Except for the burnt fuel.

But you should know that cars burn a lot of fuel only when they are pushed hard. So, if you don’t press the gas pedal, the car will not waste a lot of gas. But how much gas my car will waste in an hour?

Good question. On average, a vehicle would waste ¼ gallon of gas on smaller displacement engines. Larger displacement engines can waste even up to ½ gallons per hour. But why is my car idling high? More on that in a moment.

High Idle Situations

Now let’s move on with the topic and learn more about the situations that you will face when you are facing a high idle and you are looking for an answer to the question of why is my car idling high.

There are a number of these situations and this is why we are going to make sure that we cover all of them so you see if this is one of the situations that you are in. So, let’s get into it.

1. High Idle On Cold Start

Before we dive into why is my car idling high, let’s take a look at the situation when you have a high idle at start up.

Many people think that they have a problem when they cold start their vehicles. But in reality, this isn’t the case.

Why Is My Car Idling High

This is a completely normal situation. The RPMs at the startup are higher, the engine needs a bit of throttle and extra gas to warm up quicker.

If you don’t have a high idle at start, the engine will probably stall. So, don’t be afraid if the RPM goes to 1,200 because after the engine warms up this number will drop to 800 RPM.

2. High Idle In Park And Neutral

Now let’s cover another situation before we dive into why is my car idling high. And that is the high idle in park and neutral.

If this is the case, and you have a high idle in park after the engine is warmed up, then you have a problem. And you should sort this problem out.

This is why in the following chapters, we are going to list the most common causes and how you can diagnose and sort out the issues. But before that, let’s cover the last situation.

3. RPM Going Up And Down At Idle

Now let’s cover the last quite common situation when you have high idle. And this is the case when RPM goes up and down at idle.

As we mentioned, the RPM should not fluctuate. They should be high as 1,200 RPM when the engine starts and they should drop after the engine warms up.

If this happens on a regular basis. It is important to act quickly and learn why is my car idling high. And this is what we are going to cover in the following chapters, where we are going to cover all the possibilities when it comes to this issue on your car and we will learn how to solve it. So, you definitely don’t want to miss that.

Why Is My Car Idling High

Since we learned all about the possible situations when you can have a high idle, we think that now it is time to dive into the causes of high idle.

We need to learn why is my car idling high and cover all of the different possibilities for this problem ever occurring on your vehicle. This is why all the following chapters will be dedicated to this and you don’t want to miss that. So, let’s get started.

Why Is My Car Idling High, Causes #1: Blown IAC Fuse

Now let’s dive into the causes of why is my car idling high. We will start with the most basic problems that you could come across that could cause you an issue like this.

And the most basic problem is a blown IAC fuse. So, what is the IAC fuse? Well, this is a tiny fuse located in the fusebox.

This fuse basically controls the idle air control valve. The idle air control valve is the component that is in charge of the idle speed of the engine on some vehicles. It is mainly found in cars from the 90s era. More in-depth we are going to elaborate in the next chapter.

What happens in this situation is that this IAC fuse can fail and when it fails the idle air control valve starts to malfunction. Once the IAC valve malfunctions, you can expect problems like the car stalling or the engine running on high RPM like in this situation.

This problem will basically cause the IAC to stay either open or closed. And when you have an open IAC you will have a high idling speed of the engine.

What is important for you is to check the IAC valve fuse. You can do this by locating it in the fusebox. If it’s burnt, then just replaced it. This will hopefully solve your problem of why is my car idling high.

Why Is My Car Idling High, Causes #2: Bad Idle Air Control Valve

Now let’s move on and cover the next cause of why is my car idling high and that is the bad IAC valve.

In the previous chapter, we have covered a lot about the IAC valve and learned that this valve basically controls the intake and this valve allows more air to enter into the combustion chamber at startup so a richer air-to-fuel mixture is created.

This is quite an essential thing, mainly because the engine is cold and when an engine is cold, running lean is not something that you want. You need good combustion, so the engine doesn’t stall.

And this idler air control valve does precisely that, at startup, it opens to allow more air to enter the combustion and after a few minutes and the engine is warmed up, it should close.

And what can happen is that this idle air control valve could stay open or closed permanently. In this situation, the IAC valve has failed. It is not working anymore.

So, when you have a problem like this, you will either have problems with high RPM like you do, or problems with low RPM when the engine cold starts.

Both of these situations are not good and you need to solve this problem if you want to avoid any possible issues down the line. Mainly because this can worsen your fuel economy and also potentially affect other components inside of the engine. These two reasons are the most common causes why is my car idling high. Now let’s move on to the next probable causes.

Why Is My Car Idling High, Causes #3: Vacuum Leaks

The next probable cause for the problem of why is my car idling high is the vacuum leaks. So, what is a vacuum leak? This question confuses a ton of people and this is why it deserves a good answer. So, let’s elaborate on it.

A vacuum leak in simple terms means that there is unmetered air that is entering inside of the intake. So, what is unmetered air? You might notice this if you’re seeing a P0113 Ford error code.

Well, unmetered air is simply air that has not been checked by the MAF sensor (to learn more, check out our guide on what is a MAF sensor). If you didn’t know, on the intake usually there are MAF or MAP sensors that evaluate the air that enters the intake and they help the engine to adjust the air to fuel ratio.

And when there is the air that enters unmonitored inside of the engine, it could cause situations like in this case with the high idle RPMs.

And when it comes to places that can cause leaks, we can say that there are plenty of them. And what is most frustrating is that finding vacuum leaks is very difficult and can be done only with a smoke machine.

Without a smoke machine, you can only guess what could be the reason for the problem. And there could be a lot of these reasons. Namely, intake manifold crack, intake manifold gasket leak, bad PCV valve, EVAP system leaks, or simply some of the rubber hoses have failed.

The simplest thing you can do is to replace the PCV valve. These valves are rather cheap and affordable. So, you can snatch one of these for a really good deal.

So, this is also a very common cause of why is my car idling high. Now let’s move on to the next probable cause.

Why Is My Car Idling High, Causes #4: Bad Engine Coolant Temperature (ECT) Sensor

Now let’s move on to the next cause of why is my car idling high. And this is the ECT sensor. Also known as engine coolant temperature sensor. So, what does this sensor has to do with the high idle? Well, it has a lot to do with the idle speed of the car.

The ECT sensor is monitoring the temperature of the coolant. So, when you do a cold start the sensor knows that the coolant is cold and tells the engine to run a bit rich till the engine reaches operating temperature. And this is the case when you have high RPM at the startup.

Then the ECT sensor will notice that the temperatures have reached normal operating temperature and will send this information to the computer. And then the computer will readjust the air-to-fuel ratio back to normal. So, the RPM will drop.

So, what can happen in these situations is that the ECT sensor could stay in a fully cold position and thinks that the temperature of the coolant is really low. When this happens, the car will continue driving at high RPM and you will be asking yourself why is my car idling high.

This is another very cheap part that can be replaced with a wrench. The ECT sensor is usually bolted onto the block of the engine. This is why finding the component might be tricky because not all engines are the same. You can learn more about this in our guide on the Honda Civic P0128 code and the P0128 Jeep code, or the PO128 code.

Why Is My Car Idling High, Causes #5: Bad Throttle Linkage

The next probable cause of why is my car idling high is issues with the throttle linkage. This linkage is present on older vehicles that are running carburetors and old-school throttle bodies.

What can happen is that the cable can cause issues. The cable as you know is the input that you give to the carburetor or the throttle body to open and close.

And if this mechanism has failed this might be the core of your problem. Just try to move the cable manually and there should be a little bit of play. If the cable is too stiff it might be preventing the throttle to close. Thus the idle will increase. In some instances, you will need to replace the cable.

Why Is My Car Idling High, Causes #6: Faulty Carburetor

Now let’s cover the last probable cause why is my car idling high. And this is because of a bad carburetor.

If you are running an older vehicle that has a carburetor and is not computerized. The only place where you should look for the problem is either in the carburetor or the throttle linkage that we covered previously.

Carburetors are really complex devices that can cause a number of issues like in this case. In fact, there could be three things that could make your carburetor work like this.

Why Is My Car Idling High

The first thing is the misadjusted idle speed. On each carburetor, there are idle screws that you turn in order to adjust the idle speed of the engine.

The second thing is the clogged idle passage. When you have a problem like this it is highly likely that you will have less fuel and an increased intake of air, which will lead to high idle.

And the third issue is a problem with the fast idle cam. But how you can diagnose why is my car idling high? More on that we will cover next.

How To Diagnose Why Is My Car Idling High

Now let’s take a look at how you can diagnose this problem with why is my car idling high. What you can do to tackle this problem?

The first thing you would want to do is to grab an OBD2 scanner and plug it in if you own a vehicle that has this port. Then scan the car for codes. If the IAC valve, ECT sensor, or you have a vacuum leak, it should cause errors in the system.

If there are error codes, make sure that you pay close attention to them and study them closely. Or if you are solving the problem blindfolded without a scanner, you can check the fuses and see if the IAC fuse is good.

You can also test the IAC valve and the ECT sensor with a multimeter if you have one around. Overall, that’s what you can do without tools. But how much it will cost you to sort this problem out? Let’s cover more on that next.

Cost To Fix High Idle

So, how much it will cost you to fix why is my car idling high? Well, it shouldn’t be very expensive. A simple PCV valve, ECT sensor, IAC valve, or fuse does not cost a whole fortune.

About $150 will probably be the right price for this repair. If you have diagnostics tools, you can do this much cheaper and pay only for the part.


In this article, we have covered quite a bit when it comes to the problem of why is my car idling high. First, we learned what is high idle and the situations where you will notice a problem like this.

Then, we moved on and started learning why is my car idling high. We have covered all the different causes of this problem. Lastly, we covered some of the methods that you can try to diagnose and fix the problem.


Now let’s answer some frequently asked questions.

What Is RPM In A Car

RPM refers to revolutions per minute. In other words, how many revolutions the crankshaft makes in a single minute. This number can vary from 800 to 6,500 RPM in most engines. Some engines rev even higher than this.

Is Idling Bad For Your Car

Idling is not bad for your car, you can idle the engine as much as you want and there will be no damage done to it. Except for the fuel spent while idling.

What RPM Should My Car Idle At

Most engines idle at 800 RPM nowadays. Anything less than 800 RPM will potentially cause the engine to stall and then you will have to crank it again.

Why Is My Car Idle High

Cars usually idle high because of a bad IAC valve or bad IAC valve fuse. Sometimes they idle high because of a bad ECT sensor. Sometimes because of vacuum leaks. The problem needs to be properly diagnosed to know for sure what is causing the issue.

What Causes Rough Idle

Rough idle is caused by a number of reasons. But in most cases, this problem is caused by bad spark plugs, bad ignition coils, and vacuum leaks.

Why Does My RPM Go Up And Down While Parked

There could be many reasons behind the rough idle of your car. But the most common ones are ignition problems. Namely, issues with the spark plugs and coils. Also, problems with vacuum leaks and fuel delivery issues can cause this problem as well.

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