Car Is Revving In Park? Here’s How To Fix It

There is probably a problem with one of the parts connected to your engine or a problem with one of the sensors needed to keep your engine running if your engine’s RPMs are bouncing up and down and your machine can’t maintain a consistent idle speed.

But fortunately for you, the majority of issues brought on by a rough idle or your automobile revving up and down irregularly may be rectified for not too much money. And good news for you – if you know how to work a wrench and troubleshoot various automotive parts, you can DIY-fix most engine idle problems.

List 8 Common Issues Why A Car Would Be Revving In The Park

1.     Dirty/Sticking Throttle Body

Your automobile may also be revving excessively on its own due to a filthy or stuck throttle body valve. Depending on how much throttle is provided, a car’s throttle body valve will either open or close, letting more or less air into the engine.

The throttle body valve only opens partially when cruising, allowing a limited amount of air to enter the engine. The throttle body valve will fully open at full throttle to let the most air possible into the machine.

The throttle body valve can become clogged with dirt over time, causing it to stick open or close partially, which can cause your car’s engine to rev irregularly and cause the idle to jump up and down. The throttle body of most cars can be cleaned with throttle body cleaning to restore the throttle body valve’s ability to move freely.

Auto technician cleaning air throttle of the car.

A complete throttle body replacement may be required if it doesn’t resolve your engine idling problems.

2.     Dirty Mass Air Flow Sensor

A dirty mass air flow sensor is one factor that could be causing your car’s engine to idle up and down on its own. The mass air flow sensor connected to your vehicle’s engine is intended to measure the volume of air passing through the engine’s throttle valve and air intake.

This information is then transmitted to the engine’s computer, determining how much fuel to inject into the engine’s cylinders to ignite the proper air/fuel mixture. The mass air flow sensor, often known as the MAF sensor, can get dirty or clogged with debris over time.

This dirt and debris may make it difficult for the MAF sensor to measure how much air enters the engine accurately. The good news is that you can usually clean your MAF sensor to restore its ability to measure airflow.

Just be sure that the cleaner you choose to wash your MAF sensor is intended for use on mass air flow sensors. Mass airflow sensors can be cleaned with a spray made by CRC that won’t leave behind any film that might endanger the mass air flow sensor.

3.     Vacuum Leak

A vacuum leak from one of the several systems related to your engine is another potential cause of your car revving on its own.

The engine in your vehicle can be compared to a big pump that draws in air, compresses it, and then ignites it to send power to the wheels. Manufacturers of automobiles have discovered over time that your engine creates a vacuum as it draws in outside air.

The manufacturer might then use the engine’s vacuum for different power systems within the car. The brakes, EVAP, and EGR, run on vacuum lines. Because of this, you can see a lot of vacuum lines coming out of your engine’s intake manifold.

Rubber vacuum hoses and lines tend to dry out and crack over time. When this occurs, air may be able to escape via the fractured vacuum lines, and your engine’s air/fuel ratios may differ from what your mass air flow sensor detects.

Since a vacuum hose is only a short section of rubber tubing, replacing one is often inexpensive. The bad news about vacuum leaks is that it can occasionally be challenging to identify the hose responsible for them. To check for a change in your engine idle speed, you should run a smoke test or spritz carb cleaning into your vacuum lines.

4.     Bad Oxygen or O2 Sensor

The mechanical system in your car is intricate. The car’s computer needs to know how much air and gasoline the engine releases into your exhaust system.

This is achieved by measuring the amount of air flowing from your engine’s exhaust ports using an oxygen sensor mounted in the exhaust manifold or catalytic converter. So that the machine can continue to run effectively, the car’s computer can modify the air/fuel ratio.

Close up photo of oxygen sensor from the exhaust system.

As the burned air/fuel mixture passes through your oxygen (also known as O2 sensors) over time, it may become clogged with carbon deposits. Eventually, the oxygen sensors may become so filthy that they are unable to read anything or may stop reading at all.

The good news is that replacing O2 sensors typically costs little and costs less than $100. Usually, a check engine light will usually come on in your car if your O2 sensors fail. If your O2 sensor malfunctions, you can read the check engine codes with an OBD2 scanner.

5.     Bad Throttle Body Valve Position Sensor

Throttle bodies are in two primary varieties; one uses a drive-by cable system, which physically opens and closes the throttle body valve.

The other employs sensors to establish the throttle position and then electronically opens and closes the throttle body valve, known as a drive-by-wire system. It’s likely that if you purchased a vehicle within the last ten years, it used an electronic drive-by-wire system with a throttle body valve position sensor to detect whether it was open or closed.

The throttle body position sensor must be changed if it stops functioning entirely or becomes clogged with debris over time. Sometimes it might be challenging to identify when the throttle body position sensor has to be replaced in conjunction with the throttle body.

Depending on how your particular throttle body was constructed, you might be fortunate and be able to remove the throttle body position sensor separately from the throttle body.

6.     Plugged/Malfunctioning EGR Valve

A clogged EGR valve is another potential cause of a rough idle or your automobile revving up and down on its own. Your EGR (Exhaust Gas Recirculation) system, created to help manufacturers meet ever-rising pollution rules, is connected to your EGR valve.

In essence, your EGR system routes exhaust gases that would have gone through your exhaust pipe back through your engine. This limits the number of hazardous gases that are released into the environment.

The EGR valve may become clogged with carbon due to the accumulation of exhaust gasses over time, making it difficult to open and close properly. When this occurs, your engine may idle poorly and rev erratically.

The good news is that most amateur mechanics can repair your car’s EGR valve for a reasonable price as long as you have simple access to the necessary component. Since they are not all constructed the same, it is a good idea to research a replacement EGR valve for your car before buying one.

7.     Faulty Car Computer

Your car’s harsh idle may occasionally result from a malfunctioning engine computer. Engine computers, often known as PCMs, ECUs, or ECMs, all perform the same function: to interpret data from your car’s numerous systems to keep your engine operating.

Performing car diagnostics.

The ECU/PCM of your automobile may only be functioning correctly if it has access to all the data given to it. Your engine’s idle speed may dramatically increase or drop due to ECU issues, and your car may even struggle to start. Unfortunately, there isn’t a simple cure for auto computer issues; a dealer typically needs to replace and reflash the computer.

As you can expect, this repair is not inexpensive and might cost hundreds or even thousands of dollars, depending on the manufacturer and model of your car.

8.     Frayed or Disconnected Wiring

In some instances, the wiring harness that sends data to the computer in your automobile is the real cause of your car revving up and down rather than any sensor or component. Electrical wires can tear if they grow hard and brittle over time. As a result, your car’s numerous sensors may produce inconsistent behavior or data.

If your automobile is having issues revving, look for evidence of wear in the wire coming from the various sensors in your engine bay. The best course of action is to replace the wiring with new, fully insulated wires if you find that a wire appears to be fraying or showing indications of cracking.

Does Revving The Engine In Park Damage It?

As long as the engine is warmed to working temperature and you maintain the engine’s RPMs within the permitted operating range, revving the engine while the car is in the park is acceptable.

You won’t harm the engine by revving it while it’s in the park if it runs at average operating temperature and its RPMs are kept below its redline. However, if you overrev the engine right after a cold start, you most definitely run the risk of damaging the engine.

The ECU of a modern vehicle controls the engine’s cold idle speed (electronic control unit). The ECU will regulate the idle speed so that the engine heats up as rapidly as possible while keeping it from being too fast to cause excessive engine wear.

If you want to prevent premature wear, it’s crucial to let your engine warm up entirely before revving it since, in cold temperatures, engine oil may not flow efficiently. Premature wear results from cold engine oil not flowing through the engine quickly enough to lubricate all wear points effectively.

A lack of sufficient lubrication can cause parts, including piston rings, cylinder walls, rod bearings, and camshaft lobes, to wear out prematurely.


In general, it was revving a car’s engine while in the park won’t harm it, which is okay. If you over-rev an engine, which is when you accelerate a machine past its redline, you could run into issues. An engine is put under more load than it was designed to handle when it is overrevved.

Additionally, revving an engine in the park wastes gasoline and puts extra strain on the machine. A transmission can also be harmed by over-revving if it is put into drive before the RPMs have reached the average idle level.

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About Brock Rangel

Hi, I am Brock, and I am the lead editor/photographer for TheCarColony. I have been a mechanic for over 14 years now, and I am here to spread my car knowledge across the web!

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