Key Takeaways

  • Idle Air control valves can cause revving while in park.
  • Clean your EGR valve and this may fix revving while in park.
  • Throttle position sensors report the position of a throttle to the vehicle’s computer.
  • Test for vacuum leaks with brake clean.
  • Clean your throttle body the correct way to stop revving while in park.

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A car revving while in park can be scary and worrisome. So why is your car revving in park and what can you do about it?

Your car could be revving in park for a number of reasons. While the reasons may differ, consider checking these items first:

  • Idle Air Control Valve
  • Exhaust Gas Recirculation
  • Throttle Position Sensor
  • Vacuum Leaks
  • Dirty Mass Airflow Sensor

I’m a mechanic with five years experience diagnosing and repairing vehicles. I’ve received my degree in automotive repair and I am ASE certified. I receive regular training on the most recently released automotive technology. And I repair and diagnose vehicles with the most up to date tools and software.

Table of Contents

Car Is Revving In Park

When your car revs in park it can be a scary event.

It’s like someone is giving your car gas when you aren’t doing anything to your car.

This makes it seem like the car is beyond your control. But there are some common reasons as to why  your car would do this and some common fixes. Let’s take a look.

Idle Air Control Valve (IAC)

The idle air control valve was invented to automate the process of adjusting the throttle position on your throttle body.

Prior to idle air control valves, a car owner would have to manually adjust a throttle body by applying torque to an adjusting screw.

This screw would open or close the throttle plate gap while in the idle position.

If the screw opened the throttle plate, more air flow would be introduced to the engine during idle.

If the screw closed the throttle plate, less air would be allowed into the engine during idle speed.

This process of screwing the throttle plate opened or closed was automated by the Idle Air Control valve. The Idle Air Control valve (IAC) is another small little throttle that opens or closes electronically based on atmospheric conditions, as well as engine load.

If your IAC gets clogged, or fails electronically, it can cause your vehicle to rev in park. This will cause your vehicle to sporadically rev.

To fix this, you can either clean your IAC valve or replace it. Sometimes replacing an IAC valve requires you to have to replace the whole throttle body.

If your throttle body is controlled by wire, you will have to be extra careful when you replace the entire throttle body.

Exhaust Gas Recirculation (EGR)

EGR systems work by recirculating exhaust gas back into the engine’s air flow.

The EGR system takes exhaust gas and reroutes it back to the intake manifold where the exhaust gas can cool peak combustion temperatures.

The purpose of the EGR system is to cut down on the amount of pollution your car makes.

The actual EGR valve’s job is to regulate the amount of exhaust gas that is returned from the exhaust to the intake manifold.

If the EGR valve becomes clogged or fails electronically, you run the risk of overfilling the car’s intake with exhaust gas.

When your vehicle has extra exhaust gas in its air intake it can cause the car to idle roughly or open the throttle valve to get more clean air in. This will cause the car to rev while in park.

To clean your EGR this first step is to remove it. With the EGR valve removed, get some throttle body cleaner and spray it inside both the intake and outtake ports of the valve. This will clean the pintle inside the valve.

Let the liquid soak inside the valve for a couple hours before you reattach it to the car and start the engine.  To replace your EGR valve, just remove it and replace it with a new one.

Throttle Position Sensor (TPS)

Your throttle body position sensor is responsible for measuring the position of your throttle.

Your throttle controls the amount of air that’s introduced to your engine.

When the throttle is wide open, more air can flow through the throttle. When the throttle is closed, less air flows through.

The job of the TPS is to report the position of the throttle to the vehicle’s computer.

The throttle position sensor will take into account the position of a throttle and change the engine’s performance based on the data it receives.

For example, if it sees the car’s throttle body valve is wide open, the computer will dump more fuel into the engine.

If the sensor reads that the throttle is closed, it will tell the computer to use small amounts of fuel.

If your TPS is damaged or reading incorrectly, it can cause the computer to add more fuel to the vehicle during idle time causing the vehicle to rev while in park.

To fix a faulty throttle position sensor, you can try cleaning the throttle or replace the item.

Replacing a TPS is relatively simple.

Just remove the two bolts holding the sensor in and remove the sensor.

Replace the sensor by reversing the steps.

Cleaning your throttle can fix your TPS issue, but when you have TPS issues, you usually need to replace the TPS.

Vacuum Leaks

As your engine runs, it creates vacuum in the manifold.

The vacuum comes from the intake stroke of the engine’s combustion process. The engine is sealed so well that intake strokes create a vacuum inside the manifold.

This vacuum is crucial to an engine’s operation. If for some reason your engine starts to leak vacuum, unregulated air will become introduced to the engine. This will cause your engine to rev while in park.

Vacuum leaks are usually easy to identify by lifting the hood and looking for loose vacuum connections. For example, if a brake booster hose becomes disconnected you will see this if you look at the car’s engine.

If you are looking for vacuum leaks and cannot find them, start spraying brake clean around the engine bay.

When the brake clean is sucked into the engine through a vacuum leak, the engine idle speed will increase.

This process will help you narrow down the location of the vacuum leak without having to constantly hit the gas pedal.

Mass Air Flow Sensor

The mass air flow sensor (MAF) in a car measures the temperature and amount of air your car is intaking.

A MAF sensor is usually located somewhere between the throttle and intake manifold.

The MAF sensor communicates the amount of air intake a vehicle is experiencing to the vehicle’s computer.

Then the vehicle computer decides how much fuel should be applied to the engine and regulates the air being inserted into the engine cylinders.

The MAF sensor also works in coordination with an oxygen sensor.

The MAF sensor measures intake by heating up a wire and measuring the amount of voltage that’s generated by the wire as air passes over it.

If the MAF sensor is reading incorrectly due to it being unplugged or it failing, it will cause the computer to send out the wrong information, in turn, revving your car while in park.

To fix the issue of a bad MAF sensor the solution is to usually replace the sensor. You can try cleaning it with an electronics cleaner, but this solution does not usually work.

As well, MAF sensors can become unplugged when someone pulls the air filter.

Check that the MAF sensor is plugged in before you replace it. Sometimes, you just have to hook up the unplugged sensor and everything will start working correctly.

Cleaning Your Throttle Body

Your vehicle's throttle body valve is an important component to your vehicle’s engine.

Without it, your vehicle would be running at max speed all the time. So it’s important to clean the throttle body every once in a while.

Cleaning your throttle body may also fix a car that’s revving in park. Here are some steps to clean your throttle body.

  • Gather necessary tools: You will need a screwdriver, a cleaning solution (such as throttle body cleaner or carburetor cleaner), a clean rag or shop towel, and possibly a new gasket for the throttle body.
  • Disconnect the intake hose: Use the screwdriver to loosen and remove the clamp that holds the intake hose to the throttle body. Pull the hose off the throttle body and set it aside.
  • Spray the cleaning solution: Spray the cleaning solution directly into the throttle body, being careful not to spray it onto any electrical components or sensors. Let the solution soak for a few minutes.
  • Scrub the throttle body: Use the rag or shop towel to scrub the inside of the throttle body, paying special attention to the throttle and the edges of the walls. You may need to use a toothbrush or other small brush to get into tight spaces.
  • Wipe away the grime: Use the clean rag or shop towel to wipe away any grime or dirt that you scrubbed off the throttle body. Be sure to remove all of the cleaning solution.
My Car Is Revving In Park (Causes & How To Fix)

About The Author

Christopher Sparks

Christopher Sparks

Christopher Sparks has been servicing vehicles since 2012. After completing the automotive studies program at Camden County College, he was awarded an Associates's Degree in Applied Science. His first job was a lube-tech at Jiffy Lube, and is currently an independent B-Technician servicing vehicles for the United States Postal Service. Christopher is ASE certified and loves rebuilding engines.

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