Are you noticing some strange action when it comes to the RPM gauge on your car and you ask yourself at what RPM should car idle at? Well, if that is the case, then you are at the right place because there will be a lot to cover on this topic and we are going to cover all you need to know when it comes to this problem.
Doing the proper research before you jump to conclusions when it comes to the tachometer and the weird readings that you get are importnat. There are a couple of different conditions that could be it and you need to be aware of each one of them.
Mainly because each problem can have different causes and can be triggered by different things. So, knowing the causes and the types of idle should be your top priority. Also, the diagnostics approach is quite different for each one of them. But you shouldn’t worry because we will do our best to try and help you out with solving your problem. Now let’s see what we are going to cover in this article.
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First, we are going to learn what is engine RPM and on what RPM should car idle at. Then we will cover the different types of idle that you will come across when it comes to running your vehicle. And after that, we will cover the causes of rough, low, and high idle. Then we will move on to diagnosing and learn more about how you can diagnose the problems. So, if you want to learn more, follow along.
What Is Engine RPM
Now before we dive into the nitty gritty stuff and understand what RPM should car idle at. Let’s first learn more about what is engine RPM in general and where you can find this information. There are a ton of people who might have similar problems. So, this chapter is dedicated to them to get things going.
So, what is engine RPM? Well, every internal combustion engine runs at certain RPMs. The RPM in other words is the revolutions per minute. But what does this mean?
Well, this means that the engine is measuring the rotations of the crankshaft. Each rotation is an RPM and revolution.
This means that the engine car spins about 7,000 times in a single minute. Which is a crazy number. But for many engines, this use can be detrimental to the engine’s health if done very often.
The ideal work of the engine is somewhere between 2,000 and 3,500 RPM while the car is moving. Running the engine at moderate RPM will also improve your fuel economy and your car will not drink a ton of gas. But where is this information available?
Well, each car has a tachometer that is installed on the gauge cluster. In the past, this was an option. But nowadays all modern cars have one. The tachometer is found next to the speedometer and you will see numbers from 1 to 7 if your engine is running to 7,000 RPM or 1 to 8 if the engine is a high-revving engine and can run to 8,000 RPM.
What RPM Should Car Idle At
Now let’s dive into the problem and learn more about what RPM should car idle at. What is the idle RPM for each car out there?
The idle RPM really depends on the car manufacturer mostly. But the range is between 600 and 800 RPM.
On a cold start, the RPM could be 1,000 or higher in some applications. But once the engine warms up properly, the RPM should drop to 800 and be stable at this RPM.
Anything below or above the factory recommended idle speed, is considered to be a bad idle. More on bad idle we are going to elaborate later on in the article where we are going to cover all the types of idle.
The second most important thing to know is that if you have a situation when the engine drops the RPM quite significantly let’s say below 600, there is a high risk of the engine to stall. This means to shut off completely and ruin your day.
But how to find the specific idle RPM number for your engine? Well, if the engine does not have any issues and is idling correctly, then this is probably the right idle RPM for that specific engine. Another way you have a problem. So, we learned on what RPM should car idle at. Now let’s see the types of idle.
Types Of Idle
So, we have covered at what RPM should car idle at. We think that now it is time to cover more on the different types of idle that you can come across as a driver.
If you didn’t know, there are a few types of idle. And each of the types has separate causes. So, what we will do in the following four chapters is to cover all these types of idle and after we cover them, we will dive into the causes of these conditions. And lastly, we will share some diagnostic tips when it comes to each of these types of idle. So, if you want to learn more, follow along.
Normal Idle RPM
We covered what RPM should car idle at. Now let’s see what is the normal idle RPM. What is the normal idle RPM of an engine?
Well, as we noted previously when you start up the engine, the RPM is usually higher. About 1,000 RPM or even 1,100 RPM in some applications.
And after the engine warms up, the RPM will drop, and the RPM on which the needle drops and stabilizes is your normal idle RPM.
This RPM number also depends on the carmaker. In most cases, 800 RPM is the right normal idle RPM for many cars.
In some applications, this RPM even drops to 600. It really depends on the car and the make and model that you are running. As well as on the engine type.
But one thing is for certain when determining the normal idle RPM is the point when the idle stabilizes once the engine warms up. This is the sweet spot. If the needle does not hold still once the engine reaches the operating temperature. Then, you probably have some issues with the engine. And more on them we are going to cover next since we learned what RPM should car idle at.
Low RPM Idle
Now as we covered what RPM should car idle, we can move on to the second type of idle that is considered non-normal idle. And that is the low engine idle. But what is low engine idle?
Well, low engine idle is a situation when the RPM drops below the normal level. We noted previously that the normal RPM is at about 800 or 600 in some applications.
And in these situations when the RPM drops, the situation could lead to an engine stall. And this is something that you don’t want because you will need to restart the engine again and again, due to an engine stall.
The car could stall on you in the middle of the traffic and you will end up causing issues for other motorists. So, low RPM idle is really alarming and you should try to sort things out. More on that we are going to cover later on.
High RPM Idle
So, we covered what RPM should car idle at, now let’s discuss more about the high idle. What is high idle?
Well, high idle is a situation opposite to low engine idle. When a car is idling high, it means that it works at a higher RPM than it should.
So, in most cases, this idle is at 1,000 RPM or 1,100 RPM. On engine startup, this is completely normal since the car has to run a bit rich and on higher RPM till the engine warms up.
But if this condition stays after the engine warms up, then you have a problem. And this problem can be caused by a number of different things. We shall discuss them later on when we are going to cover the causes for each engine idle situation. So, we learned what RPM should car idle at, now let’s move on to the next type of engine idle which is the last in our case.
We learned what RPM should car idle at, now let’s take a look at the last type of idle which is often the most problematic type of engine idle.
Rough engine idle is a situation where you have a car with the needle on the tachometer going up and down all the time while the car is running.
Usually, the RPM fluctuates a little bit. For example, one hundred or two hundred RPM plus or minus.
And if you notice a situation like this, you need to react quickly because this is a big issue that should not be ignored.
The needle on the tachometer should always be nice and level. Only to respond whenever you apply the foot on the throttle and then to drop again back to normal idle RPM.
So, we learned what RPM should car idle at. Now let’s take a look at what are the causes of all these conditions. More on that, next.
Causes For Bad Idle
We covered what RPM should car idle at. Now let’s take a look at the causes of the specific problem with bad idle and car idling problems
In the following chapters, we are going to discuss the causes of low engine idle, high engine idle, and rough engine idle. So, you definitely don’t want to miss that, let’s cover them briefly and learn what are the possibilities.
1. Low Idle Causes
Now as we learned what RPM should car idle at and learned that the ideal RPM is at about 800, we can slowly move forward and learn more about the low idle causes. What can cause a car to idle low and possibly stall?
Well, there are a few possibilities when it comes to this problem with your car. The main reason is probably the idle air control valve. This valve is specifically designed to control the idle on cars that were manufactured before the electronic throttle bodies were a thing.
And what can happen is that this IAC valve or its fuse can fail and cause problems like in our case with the low engine idle. So, it is advised that you remove it and give it a good cleaning. This often sorts out the problem.
Or if you have a more modern vehicle, you should check the throttle body and see if there is any carbon buildup inside. If there is dirt inside of the throttle body, clean it well with carb cleaner. This will hopefully sort out the issue.
Also, in this case, the TPS sensor that is mounted on the throttle body is a good idea to be checked. The TPS sensor is basically the throttle position sensor (aka the throttle body sensor). If this sensor is not working well, then you might have a problem with high or low engine idle.
Other causes can be the ECT sensor, vacuum leaks (you might notice error codes such as the P0113 Ford code), or ignition system problems. Now let’s move on to the next problem since we learned what RPM should car idle at.
2. High Idle Causes
Now let’s dive into the high engine idle causes since we covered what RPM should car idle at. So, which are the causes for high engine idle?
As we noted previously, this is the situation where the engine is running high and the idle engine speed is not quite normal.
This problem can be attributed to a number of reasons. But the biggest reason in older vehicles is often the bad IAC control valve that we mentioned previously or the fuse that is regulating this valve.
If your car has an IAC valve, you should definitely check it out and make sure that this component is not causing the issues.
The second thing you would want to check is the throttle body itself. Maybe the throttle body is too clogged up and is stuck in an open position. Clean it well with carb cleaner.
The next thing you would want to check is vacuum leaks. A lot of times, vacuum leaks can develop in cars and they will allow unmetered air to enter inside the engine. Unmetered air inside of the engine will result in abnormal work and also lean air to fuel mixture and higher RPM than normal.
Other possibilities that you want to check are the ignition system (spark plugs and coils), or if the car is an older model, you need to check the distributor and wires, as well as the carburetor. Now let’s move on to the next causes since we covered what RPM should car idle at.
3. Rough Idle Causes
Now since we learned what RPM should car idle at, let’s dive into the rough idle causes. So, what is a rough idle?
Well, rough idle in general is a situation when the needle of the tachometer is fluctuating up and down all the time. This problem is often caused by engine misfires. Which in other words are uneven explosions inside of the combustion chamber.
So, we can say that rough idle is quite different when compared to low or high idle since this is a situation when the RPM fluctuates quite a bit. But what could be causing this problem?
Well, this problem most commonly is caused by bad MAF or MAP sensors. These sensors are basically measuring the airflow inside the engine. So, if they malfunction, rough idle will be present. MAF sensors have all the cars (to find out more, check out our guide on what is a MAF sensor), while MAP sensors only the turbocharged or older vehicles.
The second most common cause of the rough idle is the vacuum leak. A vacuum leak can be caused by a number of things. But most commonly it is a consequence of a bad intake manifold gasket, bad EVAP solenoid, or bad PCV valve.
Other causes can include bad or dirty fuel injectors, bad fuel filters (so, be wary of the signs of a bad fuel filter), weak fuel pumps, or carburetor issues if your car is running a carburetor. So, we learned what RPM should car idle at and the causes for bad idle. Now let’s take a look at how to diagnose this condition and share some tips with you on it.
How To Diagnose Bad Idle
Now we know what RPM should car idle at and what is considered to be a bad idle. So, how you can diagnose bad idle?
Well, if the idle does not fall at 800 RPM a few minutes after a cold start, this type of idle is considered to be high idle. The main causes for this problem are a bad IAC valve or IAC fuse, a bad throttle body, or a TPS sensor if the vehicle is more modern. Also, it might be a bad ECT sensor. You can learn more about this in our guide on the Honda Civic P0128 code and P0128 Jeep code, as well as the PO128 code.
If the idle RPM drop below 800 RPM and the car simply struggle to run we call this low idle. And this type of idle is also very often caused by the same components as the high idle. So, check the IAC and the fuse if you have it on your car. Or the throttle body if you own a newer vehicle.
On the other hand, if you have rough idle. In other words, in the situation where the idle moves up and down, you have a situation where you experience engine misfires.
The root cause for this situation is often the ignition system. And you should check components like the spark plugs and coils. Also, check the fuel system if the ignition works well. But most often the root cause of these problems is found in the spark plugs. Also, inspect for vacuum leaks and see if the PCV valve works well.
Conclusion To What RPM Should Car Idle At
In this article, we have covered quite a bit on the topic of what RPM should car idle at. First, we learned what is engine idle and at what RPM should car idle at.
Then we covered the types of idle and also the causes of these situations. Lastly, we shared some diagnostic tips and ideas of where to look for a specific bad idle problem.
Now let’s answer some frequently asked questions.
What Is RPM
RPM is an abbreviation that refers to revolutions per minute. And this is the number of times the crankshaft rotates per single minute while the engine is running.
What Does Idling Mean
When a car idles, it means that the car is running at normal operating RPM which is at about 800 RPM. When you press on the throttle, you break the idling RPM and increase the RPMs of the engine. In other words, the engine is not idling anymore.
What RPMs Should A Car Idle At
This really depends on the car manufacturer. But most engines idle at 800 RPM. Some of them idle lower but most of them are around this number. 600 is probably the low end.
Is Idling Bad For Your Car
Idling is not bad for your car. You can idle your engine forever and it will work fine. Still, you will have to top off the gas tank once in a while.
Is Revving Your Car Bad
Revving can be damaging to the engine. Especially if you go to the redline quite often and your engine is not a high-performance engine. Some engines simply do not like you to rev them really hard.
What Causes Rough Idle
Rough idle is often caused by misfires triggered by bad ignition components. Namely, spark plugs and ignition coils. Also, fuel system related problems can cause issues like this on your car. Something like a bad fuel filter, or bad injectors can ruin the work. In addition to this, vacuum leaks can also cause problems like these.