It can be pretty alarming to find your car RPM going up and down sporadically when you are parked or at a set of lights, and the engine is idling.
In this article, we’ll explain what RPM does, what the normal RPM is, and when you should be concerned and get your car to a technician.
The normal idle speed RPM in park – revolutions per minute – of smaller car engines is 700-900 RPM. Larger engines idle at 500-650RPM.
Most cars will sit comfortably within this range at idle. This RPM should feel stable and consistent and should not jump up and down.
Okay, let’s get into it.
When cars start in the morning, they idle at a quicker speed. Soon though, the engine heats up, and the revs settle down.
So if your car varies beyond these normal boundaries only when your car is cold or has been resting overnight you have nothing to worry about. If however, the range is above or below the ones indicated when your car is up to temperature this may indicate other problems.
The engine idle may also change depending on whether the A/C is turned on or if the vehicle is in Park/Neutral or Drive/Reverse.
We will look at these further down the article.
Modern engines have electronic control of the idle RPM, while older cars with carburetors can be manually adjusted.
We won’t focus too much on carburetors as these really have died out now and we will concentrate on more modern vehicles with diesel or petrol.
What Is RPM?
RPM is the initials of Revolutions Per Minute. The revolutions in question are the spinning of the vehicle’s crankshaft within the engine.
Most cars have an RPM gauge on the dash and sometimes you will see rather than showing 1,000 to maybe 10,000 indicated, you’ll see 1 through to 10 or higher.
If this is the gauge on your dash, add a thousand, so one becomes 1000, 5 becomes 5000, etc.
The faster your car engine is turning, the higher the RPMs. Don’t confuse how hard your engine is working with the speed of your car. As the gear changes, it might mean you are traveling faster but in a higher gear and, therefore, lower RPM because of this.
Why Is The Idling Speed Higher When I Start My Car?
Did you know your engine idles at 1250-1500 rpm when cold? (this doesn’t mean the temperature outside but rather the car engine being cold from not running for many hours) This is much higher than usual.
And when you think something is wrong, the engine eventually settles into its normal idling speed. As we’ve discussed, this is typically between 500-900 rpm for most cars.
The engine will start more quickly if there is extra fuel. So a component known as the auxiliary fuel injector adds fuel to the intake manifold when an engine is turned on.
It’s worth mentioning that the fuel may become slightly thicker in extremely cold conditions and therefore need to be pushed through the fuel lines quicker. Your car’s ECU recognizes the low temperatures and will increase the fuel flow into the engine from the fuel pump.
So to increase the engine’s idle speed, the throttle valve is opened, which can cause problems if the idle stays at its standard running rate. The car would run too rich and misfire.
To burn off the fuel on start up, the car idles at a higher speed.
This is why the engine idles at 1500 rpm and even higher.
The idle speed returns to normal once the motor has reached its operating temperature.
If it’s idling high after getting up to a warm temperature, then check
- Spark Plugs
- Cracked Vacuum pipes
- Throttle Position sensor
Should You Step On The Gas To Warm Up The Engine Quicker?
The engine’s idle speed will be higher when it is cold, so should you rev it to get it up to speed more quickly?
This isn’t a good idea because although the warm-up may be accelerated by revving the engine if the oil flow is low at idle, there may be some wear to the engine caused by not enough oil lubricating the pistons and valves.
High idle speeds can cause fuel to be wasted, is not good for the environment, and could cause an accident if you lose concentration if you take your foot off the brake while at a junction.
A car that shakes at idling speed may have a serious fault – Check out our Complete Guide To Cars Shaking At Idling Speed
What Causes High Idle Speeds When The Engine Is Up To Running Temperature?
If your car is running higher RPMs than it should, several things could be the problem. While some issues are simple to correct, others require specialist tools and a trip to a qualified mechanic.
Common Reasons The RPM is High
One of the most common causes of high or low RPM is a vacuum leak. Your car’s oxygen sensor often called the throttle body sensor will detect low levels of oxygen entering the engine and try and compensate to ensure the car does not stall. The car’s ECU -which is in effect the car’s brain- will therefore increase the RPM so stalling doesn’t happen.
Listen out for a hissing sound under the hood.
Throttle Position Sensor
Sometimes there is no vacuum leak but the throttle position sensor thinks that there is one and sends an erroneous signal to the ECU To increase the RPM so the car doesn’t stall.
Often throttle position sensors can be cleaned with throttle body cleaner, A can of compressed air, and paper towels. Because cleaning goes beyond the scope of this article I have included a link here with pictures of how to clean your throttle position sensor.
The good news is even if you have to replace this he shouldn’t said you back more than $150 including labor.
If you have an OBD2 reader -and if you haven’t they really will save you time and money- the code that will show on it to indicate issues with the throttle position sensor is P0122.
Idle Control Valve
The idle control valve often gets confused with the throttle position sensor. However, during idling, it is the idle control valve that dictates what RPM your car runs at.
The idle control valve affects the RPM only when the car is at idle whereas the throttle position sensor can on rare occasions affect the car at idle but more generally when the accelerator pedal has some pressure on it. The ICV adjusts the idle speed to ensure the RPMs don’t fall low enough to stall the car.
An effective idle control valve is good for the environment as you will use less fuel while parked. One thing to check if you’re having issues with the idle control valve is the fuse in the fuse box.
This should send a code to the ECU but not always.
Quite often, when the idle control valve needs cleaning or replacing, the engine warning light will remain illuminated well after you have turned the key to start the car.
Once again, if you have an OBD2 reader, the code you’re looking for is P0505.
Engine Control Unit Error
A computer problem could also be causing your excessive idling. The computer that controls any electronic components in your vehicle could be the issue.
A high idle speed can be caused by a misreading of the powertrain control computer. It’s time to get your car diagnostically checked for error codes, as it’s almost impossible to know exactly what is wrong without the code number.
Faulty Fuel Pump
The fuel pump Is located very close to the fuel tank at the rear of your vehicle. Like all car parts, they do fail, and when a fuel pump fails, it may not pump the correct amount of fuel from the tank along the fuel lines underneath your car to the engine.
When this happens, your engine will struggle to maintain a decent RPM meaning it will not get the correct fuel-air mixture needed to maintain a steady idle. Your car may sputter or stall out.
Often the fuel pump will just become clogged. This will happen often when the fuel filter hasn’t been changed, and sludge has got into the pump itself.
Carburetor Needs Adjusting
Older cars use a carburetor to control the mixture of gas and air inside the engine. Modern cars don’t have them.
If fitted, you can adjust the amount of fuel entering the engine or turn down the mix by inserting a screwdriver into the screw and turning clockwise. This will reduce the fuel entering the engine and the RPM as a result.
Carburetors are also prone to leak gas. If you’re smelling gas, too, then check out our article on the Reasons Why Your Car Smells of Gasoline and When It’s Time To Really Get It Looked At
Throttle Cable Stuck
If your car has one, the throttle cable can be temperamental and cause your vehicle to race in neutral. Many newer cars don’t have them.
An Overheating Engine
An engine that is running hot will idle faster than usual. Make sure you check your engine temperature gauge. If it’s high, check the coolant and ensure it’s got enough in the reservoir tank.
What Else Can Cause A High or Low RPM?
As discussed, the RPM is the speed that your crankshaft rotates. This will be slowed if more power is needed to drive the alternator, which powers many electrical components and circuits in your vehicle.
If you are running the car’s heating, air-con screen blower, electric seats, mirrors, or heated seats, this will impact the RPM showing on the gauge in the dash.
If you are concerned about the RPM being abnormal, turn on all of these systems when your car is parked and note what the RPM is. Then turn them off and notice the difference. You should easily see an RPM increase by 200 RPM once you turn all these systems off.
Is It Normal for My Car To Idle at 2000 RPM?
For all standard cars, it isn’t normal for your car to idle at 2000 RPM or above. Even in the coldest conditions, it would be abnormal to be as high as this. The highest you should really ever see, even in very cold conditions, is 1500 RPM and not 2000 RPM or above.
This indicates your car engine is working too hard to be idling while parked, and you will be using a lot more fuel than you need.
Is 500 RPM at Idle Too Low?
Absolutely not. If your car appears to be perfectly fine at 500 RPM when you are parked and isn’t shaking or stuttering you have nothing to worry about. This shows that your car engine isn’t being forced to work hard when your car is parked.
This is at the lower range of RPM for all vehicles. Anything lower than this, you may start noticing the car shake and stall.
Therefore it is worth keeping an eye on but should not cause any concerns.
If you think your engine is getting overheated, check out our article on the causes and fixes. 12 Reasons Your Car Is Overheating and Fixes
A car’s RPM should range between 500 to 900 once the engine is warm. When the engine is cold especially when you start your car in the morning this RPM can increase to over 1000 RPM before decreasing once the car engine has warmed up.