Why Does My RPM Go Up And Down When Parked? Engine Basics

Why Does My RPM Go Up And Down When Parked

Car engines need a lot of attention since they have numerous parts that need to work coherently to operate.

If any of these parts develop a problem, it will make the engine inefficient, and you might end up with a severe problem in a few weeks.

One of the most obvious signs that your engine has a problem is stuttering while driving or getting irregular RPM when idle. 

- Advertisement -

Let us get into the details and see what causes these problems and how you can fix them before it gets more serious;

Why Does My RPM Go Up and Down When Parked?

This fluctuation happens when your engine can’t stay idle, so it keeps compensating, and when it isn’t compensating, it almost shuts down. It can happen because of a sensor failure, vacuum leak, or ERG system malfunctions. 

Troubleshooting And Fixing Fluctuating RPMs

When you turn your engine on, it might have a high RPM, and it could go as high as 1500, which is too high. This can be normal, and it drops back to 800 when the engine is hot, but that might not always be the case. 

The RPM could stay high even after you drive around for a few minutes, and one of the most significant causes of this is a dirty air control valve. 

Dirt can get into the valve and make it stay open, so it passes too much air into the engine and keeps the RPMs high. 

The idle air control valve can also cause the engine to idle low, and the engine will shake and stall. 

This will happen when the valve is stuck closed, so it doesn’t allow enough air to get into the engine, which keeps the RPMs low. 

Another sign you could encounter is that the RPMs fluctuate when you put a load on the engine, for instance, turning the air conditioner or the headlights on. Stalling when you put the car in drive or reverse can also indicate a bad idle air control valve.

The biggest issue with air valves in a car engine is dirt, and you should try to clean it to see if it will help solve the problem.

You need to locate the valve, take it out and clean it and in most cars, it is relatively easy to find.

Find your air filter box and follow the intake tube to your throttle body, and the idle air control filter will be right above the pipe joint. Sometimes sits in the side or underneath; look at the general vicinity around the throttle body.

If your car is more modern, it might be using an electronic throttle body. This is a throttle body that doesn’t directly connect with the cable. 

It will have a mortar, and when you press on the gas, it will send an electrical signal that will open and close the throttle body.

If you have an electronic throttle body, odds are, you don’t have an IAC valve since you don’t need it, so the more likely problem, in this case, will be a vacuum leak. To understand why you should clean the IAC, you must know how it works.

The throttle body regulates the air that goes into the engine; giving it a little gas allows more air, which helps your car accelerate. When you floor the gas paddle, it will allow the butterfly valves to open up all the way.

When you park your car, your foot is off the gas so that the throttle body will close completely, but you still need air in the engine to keep it running. This is where the IAC comes into play since air can’t get in through the throttle plate.

There is a space before the throttle plate, which will allow the air to go up through a hole; thus, the air will go into the IAC then into another hole that leads to the intake to give the engine enough air to idle.

The IAC changes its valve size based on the system’s requirement to give you more or fewer RPMs so your car runs correctly. 

Over time, this valve will accumulate dirt, preventing it from moving efficiently; thus, you will have fluctuating RPMs.

Cleaning the air intake is simple; all you need is any carburetor or throttle body cleaner, anything that will dissolve carbon deposits. 

Also, get a toothbrush or any other small brush to get into the system, agitate the carbon, and make the cleaning thorough.

After cleaning the IAC, use a gasket when reinstalling to ensure you don’t have a vaccine leak since it will lead to the same problem. 

Tighten all the screws correctly, and now you should have an efficient air management system that won’t give you any trouble.

Importance Of Oil In High Mileage Engines

When your engine gets old, you need to take extra care to ensure it doesn’t break down. A new engine is relatively easier to maintain, but the task gets more complicated as the engine ages. Changing the oil thickness can go a long way in maintaining your engine.

This is something you need to do when your car mileage gets to about 130,000 miles, and you should consider using fully synthetic engine oil.

The reason for this is the high mileage means that there will be a lot of worn-out components in the engine.

Because of the friction as the moving parts rub on each other will wear out and become more delicate, so a thicker grade of engine oil will help manage that. 

You need to remember that it takes the more viscous oil longer to travel around the engine, so you need to give it time to warm up.

This means you need to start the engine and give it a moment for everything to circulate before driving off. 

This is particularly important for cold starts or in cold weather, so you get a smooth running engine when you drive.

Using thicker oil will cause the engine to work a bit slower, but it is almost unnoticeable and worth the trade. 

On the plus side, it will make your engine quieter, and you won’t hear any tapping in the engine; thus, your engine will have a longer life.

Car Maintenance Tips

It would be best to do some basic things for your vehicle to ensure it lasts longer and performs better. 

Here is a list of ideas you can use to make sure your engine performs well and every system in the vehicle is at its best;

1. Adding wiper fluid

Clear visibility is crucial for safe driving, and it is essential to have wiper fluid whenever you drive to clean your windscreen. 

Keep the wiper fluid full at all times to keep the windshield clean so that you can see the road clearly at all times.

If you need to, install new windshield wipers so they don’t get old and scratch the windscreen, making a more permanent problem.

2. Regularly check and replace engine oil.

Most cars have dipsticks, and you can pull them out to see how far the oil level has gone and if you need to top it off. 

This is a case where more is not better, and you need to stay in the correct range; otherwise, you might damage your engine.

Oil gets dirty over time, and you need to drain it and add clean oil to it. This time range will differ based on how you use your car so go to a mechanic for help on specifics.

3. Changing the filters

A car has several filters for oil and air that go into the engine. It would help if you cleaned these filters to keep them working to pass enough oil and air into the engine for seamless operation. 

If the air filter gets clogged, it won’t pass enough air, and your engine will be shutting down when idle or have a hard time starting. If the oil filters get clogged, you will have serious engine problems, so you must keep a close eye on them.

4. The tires

You need to check your tire pressure and ensure it is suitable for the terrain on which you operate your car. 

There will be pressure recommendations usually near the driver’s door, and you should try to adhere to them unless it is a unique situation like going off-road.

You need to get a spare tire and change flat tires whenever they happen. Know your vehicle and how long it can go before you need to change the tires and change them to keep everyone safe and your engine in the proper performance space.


Your RPM will go down during idle, most likely because of an issue with the idle airflow valve. You need to take it out and clean it to see if that will solve your problem. Add a gasket when putting it back to ensure you don’t get a leak since it can cause RPM fluctuations as well.

You can do this at home, but if you don’t trust your skills, it is a safer bet to go to a repair shop and get professional help rather than risk further damage to the vehicle.