Why does my pressure washer idle up and down? Helpful tips

Is the fluctuating idle of your pressure washer causing you concern? Rest assured, we have the solution. Let’s delve into why this happens and how you can fix it to get your pressure washer running smoothly again.

A pressure washer that idles up and down may have a clogged carburetor, bad gas, blocked fuel filter, dirty air filter, faulty spark plug, or bad unloader valve. Try cleaning the carbs and filters, replacing old gas, checking the spark plug, and adjusting the unloader valve.

Keep going to uncover the truth behind your pressure washer’s fluctuating idle. With our easy-to-follow guide, you can diagnose and fix these issues quickly. Let’s get your machine back to its peak performance.

The top 5 reasons for a pressure washer to idle up and down

The top 5 reasons for your pressure washer to idle up and down are:

● Reason 1: Restricted Carburetor

A clogged carburetor is one of the most common reasons for an engine experiencing idling problems. It supplies the air-fuel mixture to the engine. Harmful gas, dust build-up, and poor maintenance can restrict the carburetor’s jet.

Due to these blockages, the wrong air-fuel mixture in the engine can cause it to produce noises or even stop altogether. Residue from harmful gas left in the tank can create a sticky residue in the carburetor. Fuel in the tank must be refreshed regularly.

When it is older than a month or two, parts of the gas will evaporate, leaving some sticky residue. This happens especially when you have not used your machine for some time, like during the winter. I recommend draining the fuel before this period.

– The Role of Fuel Stabilizers

And use fresh fuel when you want to use it again. Another solution is to add some fuel stabilizers to the tank. Do not forget to add it to other stored gas as well. To clean the carburetor, disassemble it. Clean the carburetor and the jet with some carburetor cleaner. Ensure that all the sticky residue is removed.

If cleaning the carburetor is inadequate, use a carburetor repair kit to replace some components or install a new carburetor.

A pressure washer engine can also idle up and down due to loose screws in the carburetor. Check that all are correctly tightened.

● Reason 2: Clogged Fuel Filter

Old, lousy gas can also create a clog in the fuel filter. This can also cause the pressure washer to idle up and down. I recommend replacing the clogged fuel filter with a new one.

● Reason 3: Clogged Fuel Cap

As fuel is consumed, the level in the fuel tank lowers. To make up for this, fuel caps have small vent holes to allow air into the tank. If the vent holes are blocked, air cannot enter the tank. This creates a vacuum that can cause the engine to run rough or even stop.

You can test this by starting the engine without a fuel cap. If it is idling fine, there is a problem with the fuel gap. You can either clean the clogged vent holes. Or replace the fuel cap with a new one.

● Reason 4: Dirty Air Filter

A dirty air filter can cause a pressure washer to idle up and down. It will restrict the air coming into the carburetor and not allow the machine to run correctly.

To fix the, remove the air filter. Check if it is dirty. If it looks damaged, replace it. If your machine uses a paper air filter, you must also replace it. A foam filter can be cleaned with some warm water. Let it dry completely before mounting it back.

Check an air filter regularly. It should be part of your maintenance routine. Expect to replace an air filter annually or when it is filthy. 

● Reason 5: Problem with the Spark Plug

A pressure washer may idle up and down due to a problem with the spark plug. Examine the spark plug wires and tighten them if loose. Check for any corrosion or build-up of deposits at the edge of the plug. You can remove it by using a metal brush. If the spark plug does not look pleasing, replace it.

How do you fix a pressure washer idle up and down?

To fix the idling problem, clean the pressure washer’s carburetor. Check and replace a faulty unloader valve. Use fresh gas, and clean or replace the air filter.

● Pressure washer idle up and down: Clean the carburetor

Use the following steps to clean the carburetor:

– Step 1: Unscrew the front casing:

First, you need to unscrew the front cover to access the carburetor.

– Step 2: Detach the gas lines:

Detach the fuel lines leading to the carburetor. Drain the gas or carefully remove the clamps to avoid any gas leakage. I recommend draining the gas if it is over a few months old.

– Step 3: Remove the carburetor:

After unscrewing and detaching the fuel lines, remove the carburetor. Make some images or a small video of the process. You can use that later when assembling the carburetor.

– Step 4: Examine the jets and screws:

Check the jets and the rest of the carburetor. For unclogging and cleaning, use a carburetor cleaner liquid or spray.

– Step 5: Reassemble:

Once you have cleaned the carburetor, you need to reassemble the carburetor. Start the engine and check if it solved the idling problem.

● Pressure washer idle up and down: Inspect and replace the unloader valve

A problem with the unloader valve can be the reason for your idling problem. The engine of your pressure washer may rev sporadically because of this. To check the unloader valve, you have to disassemble it partly.

You will need to unscrew and remove the external casing of the pressure washer to see the pump. Once the pump is visible, you may see a valve with a spring-loaded plunger below the outlet valve. This is the unloader valve. Adjusting the unloader pressure valve is a tricky process.

The unloader valve adjustment aims to find the spot where the pressure is at its maximum. And the pressure spike when you release the trigger is minimal. Remove the top lock of the nuts. Clip the pressure gauge and start tightening the spring.

– How to Adjust the Spring for Optimal Pressure

Once the spring is adjusted, engage the trigger to prevent blockages in the unloader valve. Adjust the knob until you find the spot where pressure is maximal and the spike is minimal. In case you find that the pressure is not adjusting correctly, call a professional for help.

The unloader valve of a pressure washer has a tension spring which is responsible for releasing the pressurized water when the trigger is pressed. The tension spring is also responsible for decreasing the pressure when the trigger is released.

– Finding the Ideal Tension Spring Setting

By adjusting the pressure washer unloader valve, the goal is to find the ideal setting for the tension spring. Alternatively, there are 4 fixes to erratic revving that you can try. Always ensure that the pressure spike that you will see when you release the trigger is less than 10%.

A higher spike can damage the pressure washer. Cleaning up the pressure washer and checking the air filter for clogs caused by debris or dirt are some of the fixes to erratic pressure.

If these steps do not resolve the issue, it’s best to call a professional. Remember, safety is paramount when dealing with machinery.

● Pressure washer idle up and down: Add fresh fuel to the tank

Carburetor’s jets get clogged due to insufficient gas. For gas-powered pressure washers, fuel should not be left in the tank for more than a month. If it is older and you have problems, drain it from the tank and the carburetor.

Check the carburetor for any sticky residue. Remove it with some carburetor cleaner. The last step is to add some fresh gas. If you plan to store your pressure washer for over a month, add some fuel stabilizer and other stored gas to the tank.

● Pressure washer idle up and down: Clean the air filter

The air filter in a pressure washer filters the dust particles in the air. A pressure washer idling up and down can be due to an inadequate clean air supply. This can be due to a dirty air filter.

Use the following steps to clean your air filter:

– Step 1: Open the air filter lid

Open the air filter casing located next to the fuel tank and carburetor. Remove the air filter and clean the dust and debris inside the case.

– Step 2: Clean the filter

Suppose your pressure washer is using a foam air filter. Use a mixture of soap and warm water to clean it. If you can not clean it well, or it is damaged. I recommend replacing it. If your machine uses a paper air filter, always replace it.

– Step 3: Check for soap residual

After cleaning the air filter, ensure no soap residue is left. Let the filter dry completely.

– Step 4: Apply engine oil

Apply a small amount of engine oil to the filter. This will keep small dust particles from reaching the engine.

● Pressure washer idle up and down: Check the inlet hose and filters

Check the inlet hose and filter for any possible issues. Often, they contain some dirt. Clean the hose entirely. If there is any leakage, repair or replace it.

● Pressure washer idle up and down: Check the water supply

Sometimes, the water source you use may not be supplying enough water. Check the amount of water that enters the pressure washer. Most manufacturers mention that a minimum of 2 gallons per minute (GPM) is needed. But my experience is that it will function fine with a lower amount.

But expect that it requires at least 0.9 GPM. If you use a longer hose, I recommend a diameter of ¾ inches. This avoids any surging in your pressure washer. If the washer’s pressure keeps pulsing, even when using an ¾ inch hose.

Check for any blockage. Try a shorter hose with the least amount of curves. The longer the hose, the less water pressure will be at the end.

Erratic Pressure Washer Engine Revving

Suppose your pressure washer experiences some erratic engine revving. In that case, this can be due to a problem with the air filter, a gas issue, a problem with the spark plug, or an improper carburetor adjustment.

● Erratic Engine Revving: Wrong Carburetor Adjustment

A poorly adjusted pressure-washer carburetor is one of the common causes for the engine to rev erratically. Most pressure washers have one or two screws on the carburetor that can be used to adjust the carburetor.

Start the engine and let it warm to the average operating temperature. Adjust both screws equally and find the right setting. The goal is to have a smooth-running engine.

● Erratic Engine Revving: Gas Issues

When you have gas in your tank that is more than two months old, it can be harmful gas. It can lead to erratic engine revving. Drain the old gas and replace it with fresh gas. Check the carburetor and clean it when necessary.

Do not let gas in the tank for two months, or add some fuel stabilizer. Do not forget to add this also to other stored gas.

● Erratic Engine Revving: Problems with the air filter

If your engine is revving erratically, the air filter may be dirty. This may stop enough air from entering the carburetor and lead to sporadic engine revving. Check the air filter and clean it. When the air filter is damaged, you use a paper air filter. Replace it.

Also, check the hole in the fuel cap. This must be open to let air in when the engine is running. To test this, you can run the engine without a fuel cap. If it works fine, the fuel gap hole is the problem. Try to clean it with a thin metal wire.

● Erratic Engine Revving: Spark Plug Issues

If your pressure washer engine revs erratically, there can be a problem with the spark plug. Check that the spark plug wire is connected firmly.

Remove the sparkplug and check if it looks ok. Use a metal brush to clean any deposits. Replace if needed.