Can A Bad Knock Sensor Cause Rough Idle?

Knock sensors are the crucial parts of your vehicle as it monitors the engine’s combustion process. So in the situation where your vehicle has rough idle, it’s natural to think whether the knock sensors have gone bad and are creating the mess. 

Actually, yes, a bad knock sensor can cause rough idle because it delivers the wrong readings to the Electric Control Unit or the ECU. Due to this delivery of wrong signals, you’re likely to have the issue in your vehicle. 

Too little information, right? In this article, we have structured all the information that you’ll like to know. So, stay tuned with us till the end.

Can A Bad Knock Sensor Cause Rough Idle

How Does A Bad Knock Sensor Cause A Rough Idle? 

The knock sensors record knocking in all engine operating states to prevent the damage of the engine. It picks out the structure-borne vibrations from the engine block and converts this into electrical voltage signals. 

Then these electric signals are evaluated and filtered in the vehicle’s electronic control unit. When the knock sensor goes bad it sends the wrong signals to the ECU. 

The transmission of the wrong reading to the ECU, causes the ECU to think there is a knocking. Based on these wrong readings, the ECU tries to adjust the fuel injection to avoid knocking. 

It leads to a fluctuation in the fuel injection delivery; as a result of the fluctuation, there will be a power reduction and a rough idle.

Is The Bad Knock Sensor The Only Thing Causing Rough Idle?

The times when your car is showing a rough idle issue, not necessarily it’s a sign of a bad knock sensor only.

Rough idle is a common problem where different factors come into play & the exact reason needs to be diagnosed. The other reasons for rough idle include the following: 

1. Vacuum Leak

Vacuum Leak 
Vacuum Leak 

Most of the vehicle has maze hoses of vacuum for both fuel & air. Over time, the vacuum hoses may have developed leakage, causing the air to mix up with the fuel. 

If too much air is mixed up, the engine will misfire. As a result, there will be a rough idle at a higher RPM. 

2. Faulty Spark Plugs 

Spark Plugs
Spark Plugs

The spark plug receives the electrical current from the ignition coil to ignite the fuel in the combustion chamber. 

When the spark plugs of your car go bad, it starts burning fuel at an erratic rate. You will likely have a rough idle if the problem is bad enough.

3. Grimy Fuel Injector 


Fuel injectors disperse fuel at an accurate quantity to ensure the engine’s optimal performance. It’s also a root cause for poor gas mileage as well as the rough idle. 

4. Carburetor Issue


Some older vehicles use carburetors, you may experience a rough idle on your car when it goes bad. 

Usually, when you notice a rough idle as well as black smoke from the exhaust, it can be a sign of a bad carburetor. 

How Do I Know My Knock Sensor Has Gone Bad?

There are several factors that can cause the rough idle beside the bad knock sensor. Now it can be confusing to diagnose the exact fault. 

That is why, here  are some common symptoms of a bad knock sensor. If you notice any of the following signs on your vehicle, go ahead, and look over the knock sensor. 

  • Service engine lights are on & flashing
  • Poor acceleration 
  • Decreased performance of the engine 
  • Bad fuel economy 
  • Catalyst damage 
  • Lack of power 
  • Pinging noise from the engine 
  • Poor gas mileage 
  • Slow timing

What Does A Bad Knock Sensor Sound Like?

When the knock sensor has gone bad, you will likely hear sounds from your engine. Due to the bad knock sensor, the fuel & the air ignite in the cylinder instead of reaching the combustion point. 

That is why you will get a sound like a thumping or pinging noise from the engine that will gradually become louder over time.

It’s normal for the engine to knock a little while going uphill or accelerating lightly. But when you get louder noise from the engine, it’s a sign of a knock sensor failure.

How Much Will It Cost To Replace The Bad Knock Sensor? 

The replacement cost for the bad knock sensor depends on the model of the car you drive. 

Besides, your geographical region or the mechanics that you will hire to do the task will also affect the cost of the bad knock sensor replacement. 

Overall, you can expect to cost about $175- $500. The price estimated for labor is $125-$300. 

As for the parts, it’s highly dependent on the car models. The price can be between $30-$80.

Car ModelsReported Average Cost
Honda Accord $175 to $350
Ford F-150 $250 to $500
Honda Civic $185 to $385 
Ford Fusion $250 to $375
Nissan Altima $200 to $400 
Toyota Corolla $250 to $450 
Toyota Camry $275 to $500
Honda CR-V $285 to $485 

Can I Drive With A Bad Knock Sensor?

Technically yes, you can drive with a bad knock sensor. But the real question is should you do so?

The knock sensor of your car detects the detonation & preignition. This function ensures the optimum performance of the engine and no damage while you drive. 

So, when there is a bad knock sensor, you will have dip acceleration and worsened emission production. So, it’s best to get the bad one replaced.

Frequently Asked Questions (FAQs)

Hopefully, you will have a clear idea about whether the rough idle is due to the knock sensor. Still, some relatable knock sensor queries are often in owners’ minds. So here, let us try to cover some of the queries that are mostly asked in the different active forums. 

What Causes The Knock Sensor To Go Bad? 

Some potential causes, like detonation, misfire, or faulty spark plugs, lead the knock sensor to go bad. If there is any physical damage or an electrical issue, you will likely face a problem with your car. Improper handling or cold weather is also another probable cause. 

Can A Bad Knock Sensor Cause A Car To Stall?

No, a bad knock sensor can’t make a car stall or not even a hard start. So, when you are having a hard starting or stalling problem on your car, better to check the matter through experts. They will inspect the exact issue & come up with the best solution. 

Can A Knock Sensor Cause Transmission Problems?

When a faulty knock sensor on your vehicle, the engine control unit will not get the correct information on when to fire the spark plugs. Thus, it’ll cause a power loss, meaning the transmission will use different gears to compensate. 

Can A Bad Knock Sensor Damage The Engine? 

A faulty knock sensor causes many effects on your vehicle. It will also cause the PCM to misadjust your car’s ignition timing. That will result in poor engine performance of your vehicle. 

What Happens If The Knock Sensor Is Unplugged?

If the knock sensor of your car is unplugged, you are likely not getting any direct data. If the real knock of your car has gone bad, it will end up with engine damage. If it has a problem, you will get a trouble code of circuit malfunction.

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