Why Is My Car Revving In Park? Rough Idle Issues | Drive Cave (2022)

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Does your car’s engine seem to have a mind of its own revving in park or neutral without you touching the accelerator?If your engine is revving high without you touching the gas pedal or your engine can’t maintain a steady idle engine speed then this is something that needs to be addressed as if left unattended this little problem could grow into a big problem and leave you stranded on the side of the road. So what are the most likely reasons that your engine is idling rough and revving up and down on its own?

If your engine RPMs are bouncing up and down and your engine can’t maintain a steady idle speed then there is likely a problem with one of the components attached to your engine or a problem with one of the sensors used to keep your engine running.

But lucky for you, most of the problems associated with a rough idle or your car revving up and down erratically can be fixed relatively cheap. And good news for you, most engine idle problems can be fixed by most DIYers provided that you know how to turn a wrench and can troubleshoot different car components.

If your car has a check engine light this can also help point you in the right direction that way you don’t have to check multiple engine components to make sure that they are operating correctly.

Does Your Car Have A Check Engine Light?

Sometimes having a check engine light can be a blessing because it can drastically cut down on the time spent troubleshooting engine idle or rough idle issues. If your car currently has a check engine light then I’d start with hooking up an OBDII reader to the car to get a better idea of what could be causing your rough idle issues. The OBDII reader may point to an issue with a sensor or component which could be easily swapped out to see if it rectifies the issue.

If you currently don’t have a check engine light then you would need to start by troubleshooting each individual component or sensor to see which one could be causing your engine to rev up and down erratically. If you are in this camp then keep reading.

(Video) How to Fix Engine Idle Problems in Your Car (Rough Idle)

1. Dirty Mass Air Flow Sensor

One reason that your car’s engine could be idling up and down on its own is a dirty mass air flow sensor. The mass air flow sensor attached to your car’s engine is designed to sense the amount of air coming into the air intake and through the throttle valve of your engine.

That data is then sent to the computer attached to your engine so that it can then calculate how much fuel to send into your engine cylinders to create the proper air/fuel mixture to combust. Over time the mass air flow sensor or MAF sensor can become dirty or clogged with debris. This dirt and debris can prevent the MAF sensor from getting a proper reading on how much air is flowing into the engine.

The good news is that most of the time you can just clean your MAF sensor to restore its air flow reading capabilities. Just make sure that when you are cleaning your MAF sensor you are using a cleaner that is designed to be used on mass air flow sensors.

CRC makes a spray that is designed to be used on mass air flow sensors that won’t leave behind any film that could potentially damage the mass air flow sensor. I’d recommend looking up how to clean your MAF sensor on your specific make and model of car before attempting to do it yourself.

Below is a video from ChrisFix showing how to clean the MAF sensor on a Mazda Truck.

2. Dirty/Sticking Throttle Body

Another issue that could be causing your car to rev high on its own is a dirty or sticking throttle body valve. A car’s throttle body valve is designed to open and close based on how much throttle is applied to allow more or less air into the engine. While cruising the throttle body valve will only open a portion of the way to allow a small amount of air to flow into the engine. Under full throttle, the throttle body valve will open up all the way to allow max airflow into the engine.

Over time the throttle body valve can become dirty which can allow the throttle body valve to stick or not open/close all the way which can cause your car’s engine to rev erratically and can cause the engine idle to bounce up and down.

Usually, if your cars throttle body is dirty you can clean the throttle body with throttle body cleaner to allow the throttle body valve to move freely again. If that doesn’t help out your engine idling issues then the throttle body may need to be replaced altogether.

(Video) Diagnose and Fix Rough Car Idle - Main Causes For Shaking / Vibrating While at a Stop

I’d recommend checking out some youtube videos on how to properly clean a throttle body before attempting this yourself as you need to remove the throttle body from your engine intake to properly clean it. I’ve included a video below showing how to properly clean an air intake. You should also look up how to clean the air intake for your specific vehicle before attempting this on your car.

3. Bad Oxygen or O2 Sensor

Your car is a complex piece of machinery. A car’s computer needs to know how much fuel and air are being output from the engine into your exhaust system. It does this by using an oxygen sensor that is placed in the exhaust manifold or catalytic converter to determine how much air is flowing from the exhaust ports of your engine. The car’s computer can then make adjustments to the air/fuel ratio to keep the engine running efficiently.

Over time your oxygen (commonly referred to as O2 sensors) can be gummed up with carbon deposits as the burnt air/fuel mixture passes over the O2 sensor. Eventually, the O2 sensors can become so dirty that they can barely get a reading or they may stop getting an oxygen reading altogether.

The good news is that O2 sensors typically aren’t that expensive to replace and can be had for under a hundred dollars. Usually, if your O2 sensors are going bad your car will display a check engine light. You could then use an OBD2 scanner to read the check engine codes to determine if your O2 sensor is at fault.

4. Vacuum Leak

Another reason why your car could be revving on its own is a vacuum leak from one of the various systems connected to your engine. Your car’s engine can be thought of as a large pump that sucks in air and then compresses it so that it can be combusted to transfer that energy to your wheels. Vehicle manufacturers over time have learned that there is a vacuum that is created from your engine as sucks in air from the outside world.

Manufacturers could then use the vacuum created by the engine to power various systems under the hood. Systems powered by vacuum lines include the brakes, EVAP, and EGR. That’s why you may notice a bunch of vacuum lines running from the intake manifold of your engine.

These vacuum lines or hoses are made of rubber and can become brittle and crack over time. When this happens it can allow air to escape through the cracked vacuum lines which can cause the air/fuel ratios of your engine to be different from what your mass air flow sensor is reading.

Replacing a vacuum hose is typically inexpensive because it’s just a small piece of rube hose. The bad news with a vacuum leak is that it can sometimes be tough to track down which hose is causing the vacuum leak. You may have to perform a smoke test or spray carb cleaner onto your vacuum lines to listen for a change in your engine idle speed.

(Video) Car Engine Revving Up and Down? How to Diagnose Engine Surge!

The video below will show you how to perform a DIY smoke test using a cigar.

The video below will show you how to check for a vacuum leak using carburetor cleaner.

5. Plugged/Malfunctioning EGR Valve

Another reason for a rough idle or your car revving up and down on its own can be a plugged EGR valve. Your EGR valve is connected to your EGR (Exhaust Gas Recirculation) system which was developed to help manufacturers pass ever-increasing emissions standards.

Essentially your EGR system sends exhaust gasses that would have been sent out your exhaust pipe back through your engine. This prevents some of the toxic gases from being emitted out into the environment. Over time the exhaust gasses can cause a build-up of carbon which can prevent the EGR valve from opening and closing properly. When this happens it can cause your engine to idle rough and cause it to rev up and down wildly.

The good news is that replacing your EGR valve on your car typically isn’t that expensive and can be replaced by most amateur mechanics provided that you have easy enough access to the part to replace it. As always look up a replacement EGR valve for your specific vehicle before purchasing one as they are not all made the same.

Below is a video showing how to replace an EGR valve on a corvette but the process would be similar for most cars.

(Video) Engine Revving Up and Down at Idle FIXED

6. Bad Throttle Body Valve Position Sensor

There are two main types of throttle bodies, one type uses a physical cable to open and close the throttle body valve, this is called a drive-by cable system. The other type uses sensors to determine the throttle position and then open the close the throttle body valve electronically, this is called a drive-by wire system.

If you bought a car manufactured in the past decade there is a good chance that your car uses an electronic drive-by wire system with a throttle body valve position sensor to determine if the throttle body valve is opened or closed.

Over time the throttle body position sensor can get plugged up with debris or may quit working altogether and needs to be replaced. Sometimes it’s not always easy to tell that there is a problem with the throttle body position sensor and your throttle body will need to be replaced together.

You may get lucky and be able to remove the throttle body position sensor separately from the throttle body it just depends on how your specific throttle body was made.

7. Frayed or Disconnected Wiring

Sometimes the culprit for your car revving up and down isn’t a sensor or part at all but is actually the wiring harness that feeds data to your car’s computer. Over time electrical wires can become hard and brittle which can cause them to fray. This can result in inconsistent behavior or data from your vehicle’s various sensors.

If you are currently having problems with your car revving on its own check the wiring coming from the various sensors in your engine bay for signs of wear. If you do notice that a wire seems to have signs of cracking or is frayed then it’s best to have the wiring replaced with new wires that are fully insulated.

8. Faulty Car Computer

Sometimes what’s really causing your car to idle rough is a bad engine computer. Engine computers are commonly referred to as a PCM, ECU, or ECM but all do the same thing which is to interpret the data from all of the various systems of your car to keep your engine running.

If there is a problem with your ECU/PCM then your car’s computer can’t use all of the data being sent to it to keep your car running properly. Problems with a car’s ECU can cause your engine to increase or decrease the idle speed wildly, your car may even have trouble staying running.

Unfortunately, if you do have problems with your car’s computer there isn’t an easy fix, it will need to be replaced and reflashed usually by a dealer. This repair as you can imagine is not cheap and will likely come at the cost of hundreds if not into the thousands depending on your specific vehicle and manufacturer.

(Video) Rough Idle No CHECK ENGINE LIGHT~~~~ 15 minute FIX

FAQs

Why does my car rev up when in park? ›

This may be a sign of a failing throttle position sensor. The throttle position sensor (TPS) is a sensor used to monitor the throttle position of the throttle plate inside the throttle body in relation to your foot position on the gas pedal.

What sensors can cause rough idle? ›

Oxygen (O2) sensor

An oxygen sensor monitors and analyzes the amount of oxygen in a vehicle's exhaust system after combustion. A dirty, damaged or malfunctioning O2 sensor (or sensors) affects the air/fuel mixture, causing the engine to idle rough.

Why does my car rev up when idling? ›

If an engine is not getting enough fuel (this is called “running lean”), due to fuel pressure (regulated by the fuel pump and regulator), restricted fuel injectors, a vacuum leak or really anything that throws off the fuel mixture going in to the engine, this can cause the surge.

Why do my rpms go up and down while in park? ›

Worn-out or fouled spark plugs can cause rpm fluctuations. Check the engine vacuum and make sure there are no leaks. Leaks in the engine vacuum can cause rpm fluctuations. Replace the fuel filter if it is clogged or dirty.

Is it normal for a car to rev in park? ›

Answer provided by. No, revving your engine while you're in park is generally not bad. You can also rev it in neutral without hurting it—just be mindful of how much you're revving your engine, and for how long.

How much does a throttle position sensor cost? ›

The throttle position sensor cost ranges from around $40 and up, depending on your car. Find the right fit for your needs at AutoZone.

What is the most common cause of a rough idle? ›

Engine Misfires

Perhaps the single most common cause of rough idle comes in the form of a misfiring engine. As you may know, any automotive engine contains multiple cylinders. Each of these cylinders contributes to powering your car by combusting a mixture of gasoline and air.

How do you get rid of rough idle? ›

How to Fix a Car that Idles Poorly (Rough Idle) - YouTube

What can make a car rev up by itself? ›

Your car revs on its own because the engine is suddenly putting out more power than before. The problem is probably rooted in the throttle body, EGR valve, or related sensors. If it's a sudden, violent increase in revs, check out the throttle body and associated sensors first – this is probably the most likely cause.

Why does my car idle rough but drives smooth? ›

You have a rough idle if you feel the roughness when your car idles, but drives smooth. This is usually caused by a change in the amount of air going to your engine, the regularity of the ignition, your vacuum lines, and a bunch of other factors.

How do I reset my idle air control valve? ›

How to Reset an Idle Air Control Valve - Symptoms of a Bad IAC - YouTube

What causes engine over revving? ›

Most often, over-revving occurs not because of a deliberate attempt to push a vehicle, but rather as a result of missing a gear while shifting. When a manual car accidentally downshifts, a rev limiter will not be able to react quickly enough to prevent the engine from over-revving.

Why is my car revving without me touching the gas? ›

This is a common problem when the idle air control module is not functioning as it should. This is a component that helps to monitor air/fuel mixture at idle speed. When this is not working properly, this causes an imbalance in the air/fuel mixture resulting in intermittent or abnormal idling as you've described.

Can bad spark plugs cause high RPM? ›

Rough Idling

Improperly functioning spark plugs cause an uneven burn of fuel in the engine, resulting in fluctuating RPMs and a louder noise.

What happens when you rev your engine in park? ›

When you rev your engine, you place additional and unnecessary stress on your car and its engine. This is imperative when it's cold outside—revving your engine before it has had time to warm up is especially damaging, as the engine's oil hasn't had sufficient time to circulate and properly lubricate your car.

How do I reset my throttle position sensor? ›

The easiest way to reset your throttle position sensor is to unhook the negative cable from your battery for up to five minutes or to remove the fuse for your engine control module.

What happens when you unplug throttle position sensor? ›

Deteriorating fuel economy: With an unplugged throttle position sensor, the ECU cannot adequately regulate the fuel amount it sends into the engine. In turn, your fuel usage might not be as economical as advertised because the engine might be using more fuel than it requires.

How do you test a throttle position sensor? ›

You will need a multimeter to test the TPS sensor. Testing it involves grounding the connectors' terminals as you put the multimeter probe on black to negative and red to positive. Make sure the throttle is fully closed by turning the key without starting the vehicle. Then read the voltage.

Will a vacuum leak cause rough idle? ›

Vacuum Leaks Can Make Your Idle Rough and Sporadic

A vacuum leak introduces excess air into the engine, and this throws off the balance of the air and fuel. One problem that occurs because of this is a rough idle that is also sporadic.

Can a fuel pump cause rough idle? ›

What to Look For: A bad fuel pump can cause difficulty when starting the vehicle, a rough idle, and stalling. Clogged Fuel Filter – The fuel filter filters the contaminants from gasoline. Over time it can become clogged, which slows the flow of fuel. In turn, the engine doesn't receive enough fuel.

Can a faulty alternator cause rough idle? ›

If you think you have a bad alternator you should either get it checked out for sure or replace it. Autozone or Advance Automotive do this for free. It is a more comprehensive test with it removed. Yes low voltage can cause a bad idle and you may end up breaking other parts if you drive it like that.

Will new spark plugs fix rough idle? ›

Rough engine idle after replacing Spark Plugs - TOO Much Lubrication

What happens if idle air control valve is stuck open? ›

Q: What happens if idle air control valve is stuck open? If a car's idle air control valve is stuck open, it will create a rich air-fuel ratio while the vehicle idles. Therefore, the car's engine may start well while warm and run until it reaches a high enough RPM.

How is a rough idle diagnosed? ›

While some cases are less severe than others, a rough idle is usually identifiable by a shaking and bouncing sensation in the vehicle. You may also notice odd sounds, as well as inconsistent RPM counts. Normally, a vehicle should have a smooth and consistent RPM rate of around 1,000.

Can an idle control valve be cleaned? ›

Unscrew the idle air control valve by removing the screws that hold it to the throttle body. Detach any wires coming from the valve so you can remove it completely. Clean the valve by soaking it in gasoline. Move the flap in the valve while it's soaking, to ensure the gasoline reaches inside it.

Where is idle control valve located? ›

Locating the Idle Air Control Valve

The IACV is usually located on the intake manifold near the back of the throttle body. Before starting the cleaning process, be sure the vehicle is not running and that the engine is cool.

What controls the idle in a car? ›

The Idle air control valve or the IAC valve controls your engine's idle speed and is controlled by the engine's onboard engine computer system. The IAC valve controls the amount of air circulating around the closed throttle plate. It has solenoid or a valve-operating coil which opens and closes to regulate airflow.

What causes sudden unintended acceleration? ›

Sudden unintended acceleration (SUA) occurs when a vehicle suddenly begins to accelerate in speed without a driver's control. SUA happens when an electronic malfunction occurs inside of the vehicle, causing the throttle to expand and the vehicle to accelerate without the driver's intervention.

Can a PCV valve cause rough idle? ›

A PCV valve that's stuck open will allow too much air to enter the intake manifold, leading to a leaner idling fuel-air mixture. Stuck closed leads to a build up of pressure in the crank case which creates a variety of oil leaks! And this in turn can lead to a range of issues, including a rough idle.

What causes rough idle and loss of power? ›

Many system malfunctions can cause misfires or rough idling. Ignition system components, including spark plugs, plug wires, ignition coils and ignition timing are culprits as are lean air/fuel mixtures and mechanical issues within the engine.

Can you adjust air idle control valve? ›

FAST Quick Tech: How to Adjust Your IAC - YouTube

What is the code for idle air control valve? ›

What is the P0505 code? The code P0505, which stands for “Idle Control System Malfunction,” means that the computer inside the engine can't control the idle speed. As a result, the actual idle speed is not the same as the target idle speed. Most cars have a normal idle speed of between 650 and 750 rpm.

How much does it cost to fix an idle air control valve? ›

The replacement cost of an idle control valve is anywhere from $120 to $500. The cost of the parts alone will be between $70 and $400+, depending on the make and model of your vehicle. The labor cost should only be around $50 to $100 because it doesn't take that long to remove and replace the old idle control valve.

How do I stop over revving? ›

The best way to avoid over-revving if you are driving a manual transmission car and realize that you have under-shifted is to jam the clutch pedal in. When your clutch is depressed in a manual car it prevents the wheels from being connected to the engine.

Why is my RPM high but slow acceleration? ›

Fuel Filter Clogging

Another reason for your car not accelerating on high RPMs, regardless of high RPMs or not, is a dirty or even clogged fuel filter. Fuel filters are installed in a car's fuel system to filter out the dirt and the gunk in fuel.

What does it mean when your car is revving high? ›

Causes of high engine RPM while driving

It is also used to lubricate the various parts of your transmission system. If the transmission fluid begins to leak, your car will start to rev to higher levels (due to torque converter or gearbox band slippage). This may be accompanied by delayed or erratic gear shifts.

Does RPM have anything to do with transmission? ›

Cars require a transmission because their engine has a maximum RPM that it can spin at before damage occurs, known as redline (specifically, RPM is a measure of the rotating crankshaft).

Why is my car revving without accelerating? ›

If your engine revs up as you press down on the gas but your vehicle doesn't accelerate as much as you'd expect, you may be dealing with transmission slipping. If you've ever tried to accelerate on ice, where your engine revs but your vehicle goes nowhere, you know the feeling.

What does a car sound like when it needs new spark plugs? ›

Engine Knocking

Sometimes, especially while accelerating, you will hear your engine making a distinct knocking sound. That sound is caused by your spark plugs not detonating properly and igniting all the fuel. The fuel and vapor that did not ignite eventually will catch fire and detonate.

How do you know if your spark plugs are wrong? ›

If the spark plug fires at the wrong time, this could lead to constant rattling, pinging, or knocking sounds. Hard vehicle start. If your car is having trouble starting or just feels disjointed and jerky, your spark plugs may not be working right, and this can lead to misfires and erratic performance.

How do I know if my spark plugs need changing? ›

5 Signs You Need New Spark Plugs
  1. Engine Misfires. A misfiring engine is a big sign that one or more of your spark plugs are not firing properly. ...
  2. Poor Gas Mileage. When spark plugs are working correctly, they burn fuel efficiently in your engine. ...
  3. Trouble Starting. ...
  4. Slow Acceleration. ...
  5. Rough Idling.
9 Jul 2021

Why is my car revving without me touching the gas? ›

This is a common problem when the idle air control module is not functioning as it should. This is a component that helps to monitor air/fuel mixture at idle speed. When this is not working properly, this causes an imbalance in the air/fuel mixture resulting in intermittent or abnormal idling as you've described.

What causes engine over revving? ›

Most often, over-revving occurs not because of a deliberate attempt to push a vehicle, but rather as a result of missing a gear while shifting. When a manual car accidentally downshifts, a rev limiter will not be able to react quickly enough to prevent the engine from over-revving.

How do I stop my car from revving? ›

Registered. Let go of the accelerator a micro second before you push the clutch down to change gear - that will stop the revving. . Make the change and then let out the clutch fairly sharply.

Why is my car revving high but not accelerating? ›

Worn Transmission Fluid (Automatic Transmission)

Over time, the transmission fluid gathers dirt and grime. This can cause the engine to run roughly, stall or fail to accelerate when you press down on the gas pedal. You may need to have a transmission fluid change before more damage is done.

Does RPM have anything to do with transmission? ›

Cars require a transmission because their engine has a maximum RPM that it can spin at before damage occurs, known as redline (specifically, RPM is a measure of the rotating crankshaft).

How do you fix unintended acceleration? ›

Sudden Acceleration: How to stop your car if it happens to you

What causes car to idle up and down? ›

Among the potential underlying causes are vacuum leaks, EGR system malfunctions, malfunctioning oxygen sensors, dirty fuel injectors, fuel pump malfunction, faulty spark plugs, a faulty mass airflow sensor, or a faulty throttle position sensor.

What happens when you rev your engine in park? ›

When you rev your engine, you place additional and unnecessary stress on your car and its engine. This is imperative when it's cold outside—revving your engine before it has had time to warm up is especially damaging, as the engine's oil hasn't had sufficient time to circulate and properly lubricate your car.

What happens when an engine is over revved? ›

If an engine goes overspeed, commonly called "over-revving", damage to the piston and valvetrain may occur when a valve stays open longer than usual. Valve float can possibly result in loss of compression, misfire, or a valve and piston colliding with each other.

What does it mean when your car is revving high? ›

Causes of high engine RPM while driving

It is also used to lubricate the various parts of your transmission system. If the transmission fluid begins to leak, your car will start to rev to higher levels (due to torque converter or gearbox band slippage). This may be accompanied by delayed or erratic gear shifts.

How do I know when my fuel filter is bad? ›

Here are five of the bad fuel filter symptoms to watch for:
  1. You have a hard time starting car. If the problem is the fuel filter, and it isn't changed soon, you may find that your vehicle won't start at all.
  2. Misfire or rough idle. ...
  3. Vehicle stalling. ...
  4. Fuel system component failure. ...
  5. Loud noises from the fuel pump.

What can causes a rough idle at low RPM? ›

What can cause a rough idle at low rpm? The reasons for a rough idle at low rpm can be caused by a multitude of difficulties, including dirty fuel injectors, blocked air filters, faulty spark plugs, and a range of exhaust system problems.

What are the symptoms of a vacuum leak? ›

Here are four signs that your vehicle has a vacuum leak.
  • Sporadic Idling. A vacuum leak introduces excess air into the engine, and this directly affects how your engine runs. ...
  • Engine Hesitation. Your engine trouble will not be limited to your idling if you have a leak. ...
  • Vacuum Sounds. ...
  • 4 Check Engine Warning.
1 Mar 2021

What does a slipping transmission feel like? ›

A slipping transmission tends to feel like your car is jerking or surging. You might even notice that the engine revs to a high RPM between gear changes. As you are driving, the transmission should be providing constant power to the wheels.

What causes poor acceleration? ›

What Causes Acceleration Problems? Hiccups in air and fuel delivery and sensor issues are the main causes of poor acceleration. However, mechanical issues can also be the cause of low power.

How much does it cost to fix a slipping transmission? ›

This range can vary from $1,400 to $5,800, depending on your vehicle's year, make, and model. However, it may be possible to rebuild your transmission for around $1400. Finally, it some cases the slipping is caused by an electronic part which could average about $300 plus labor of $460.

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