Will a Bad EGR Valve Cause Rough Idle? (Answered!)


Your engine’s EGR valve helps to control emissions, and if it becomes clogged or damaged, it can cause all sorts of problems. But, will a bad EGR valve cause rough idle?

In this blog post, we will discuss the symptoms of a bad EGR valve and how to fix it. We will also cover some of the other causes of a rough engine, so you can get your car back on the road as quickly as possible!

Will a Bad EGR Valve Cause Rough Idle?

Will a Bad EGR Valve Cause Rough Idle (Answered!)

A bad EGR valve stuck open constantly recirculates the exhaust gases inside the combustion which take up a lot of space, not leaving too much room for fresh air to combust with fuel efficiently which leads to improper combustion and a rough idle.

If the EGR valve is stuck in the open position more exhaust gas goes into the engine intake making the engine starve for fresh air. This is where the tricky part is. The MAF sensor is responsible for measuring the amount of air flowing into the engine. The information from the sensor is then used by the engine control unit to calculate the correct amount of fuel to inject.

So, if the EGR valve is stuck open and pushes a lot of exhaust gases into the combustion chamber, the MAF sensor will measure that amount of air and will throw in the required amount of fuel for proper combustion. However, the MAF sensor doesn’t understand that this ”air” is actually not fresh air. It is actually recirculated hot exhaust gases that have less oxygen, whereas the fresh air is cooler and has more oxygen.

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At this point, the bad EGR valve has filled out the combustion chamber with recirculated exhaust gasses that are low in oxygen, and the MAF sensor has measured this air and notified the computer to send the required amount of fuel. But, the recirculated exhaust gases do not burn as well as fresh air due to the lack of oxygen, therefore, the combustion process is not proper as there is more fuel than oxygen in the combustion chamber. This results in rough idle and you can really feel the vibrations especially when the car is warmed up.

Will EGR Valve Cause Hard Starting?

Will a Bad EGR Valve Cause Rough Idle (Answered!)

When an EGR valve gets stuck open, it lets air into the intake that the engine isn’t expecting. When that happens, there’s not enough fuel for the engine to burn and that can definitely cause hard starting. The amount of oxygen coming through the EGR valve is constantly changing when you first start the car up. So, it’s difficult for the engine computer to compensate for a bad EGR.

The EGR valve takes exhaust gasses that are high in nitrous oxides and recirculates them back into the engine and it actually cools the combustion chamber and allows the engine to run better. This really helps the vehicle and the environment as it cools down the combustion chamber and therefore less NOx is produced. However, if the EGR valve is stuck open, it will constantly recirculate exhaust gases into the combustion chamber.

When you start your vehicle, the engine requires fresh air and fuel in order to start. But, the bad EGR valve will send unexpected air into the combustion chamber and will throw off the air to fuel ratio. Therefore, the vehicle will have a hard time starting.

An EGR valve can cause hard starting in a number of ways. First, if the EGR valve is not opening when it should, the engine will run leaner than normal and may misfire. Second, if the EGR valve is sticking open, exhaust gases will enter the intake manifold and dilute the air/fuel mixture. This can also lead to Lean mix symptoms like misfires. Third, a failed EGR valve can cause an unwanted vacuum leak. Any of these conditions can make it difficult to start your engine, especially if it’s cold outside.

Can You Start a Car Without EGR?

Yes, it is possible to start a car without an EGR valve. However, the engine may not run as efficiently without the valve. The EGR valve helps to regulate the amount of exhaust gas that enters the engine. Without the valve, the engine may produce more emissions. Additionally, the engine may run hotter without the EGR valve, which could cause damage over time. For these reasons, it is generally advisable to have an EGR valve in your car.

The only time you would actually want to start a car without an EGR is when you just want to drive to the repair shop. Let’s say that your EGR has malfunctioned and has left you in the middle of the road. You might know what is the problem or you have scanned your vehicle and seen some error codes associated with the EGR.

Then and only then it is advisable to drive the vehicle without an EGR. Driving without an EGR for a longer period of time will cause damage to the engine and will pollute the environment. Plus, in most states, it is actually illegal to drive without an EGR.

How Do You Test an EGR Valve Without a Vacuum Pump?

The EGR valve is an important component of the vehicle’s emission control system. It helps to reduce pollutants in exhaust gases by recirculating a portion of the exhaust gas back into the engine cylinders. Testing the EGR valve is an important part of regular maintenance for your vehicle.

There are a few different ways that you can test the EGR valve. One way is to check for proper vacuum operation with a vacuum pump. Another way is to check for proper electrical operation with an ohmmeter. But, how do you test an EGR valve without a vacuum pump? Here is how:

1. Required tools for the job

  • OBD scanner
  • Plastic straw
  • Rubber Tube (small piece)

2. Scan the vehicle to verify the problem

Before you test your EGR valve without a vacuum pump, you will need to verify that the valve is faulty. To do so, you will need to connect an OBD scanner to your vehicle’s port and hit scan.

There are quite a few OBD scan codes associated with a faulty EGR valve. Some of the most common ones are P0401, P0402, and P1404. If you’re getting any of these codes, it’s likely that your EGR valve is the culprit.

3. Open the hood and locate the EGR valve and the solenoid

Will a Bad EGR Valve Cause Rough Idle (Answered!)

The EGR valve is located in the engine compartment, usually on the side of the engine near the firewall. The EGR valve will have a vacuum line on top of it. You may need to remove other components to get to the EGR valve, such as the air intake hose or throttle body.

The vacuum line on top of the EGR valve will run to the EGR solenoid. This is how the EGR valve is operated on command. Each time the engine requires exhaust gases to be recirculated, the solenoid will open or close the EGR valve using a vacuum.

4. Disconnect the EGR valve and solenoid

Remove the vacuum line that supplies vacuum to the EGR valve simply by pulling out the rubber tube. Then, detach the connector on the EGR solenoid as well. You will notice that there are two tubes that run to the solenoid. You will need to use the bottom tube as a vacuum source for the following test.

5. Connect the plastic straw to the bottom EGR solenoid connector

Now, the bottom tube of the EGR solenoid connector will be used as a vacuum source. In it, you need to insert the plastic straw on one end and connect a rubber tube on the other end. This rubber tube will be then used to be connected to the EGR valve in order to test it.

If your EGR valve is working properly, the engine should stall when you connect the rubber tube to the EGR valve.

6. Start your vehicle

Start your engine but do not attach the makeshift vacuum source to the EGR valve yet. First, you will need to start your vehicle without it and see if it runs correctly. Just make sure that your garage door is open so the exhaust fumes can safely escape.

7. Connect the makeshift vacuum source to the EGR valve

Once you verify that your vehicle is running correctly, connect the makeshift vacuum source to the EGR valve. Once you do this, if your EGR valve is working properly, the engine should stall. If your engine doesn’t stall, then the EGR valve is faulty and has to be either cleaned or replaced.

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Hi there. I am a certified Automotive Service Excellence (ASE) mechanic since 2018 and a car detailer for 10 years.

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