How to Fix 10 Car Engine Problems (How To Fix Them)

Everything should work smoothly when your engine is running as it should. Engines can sometimes start to run rough when something goes wrong. This is especially true if the engine is idling. 

You can easily resolve a problem with a car engine experiencing a rough idle by understanding its causes. Below are 10 common reasons for an engine that is humming.

We will be discussing all causes for rough idle as well as how you can check them. Let’s begin with a quick look at the reasons.

Vacuum leaks or failed PCV valves are the main causes of rough idle. You could also experience other issues with the air-fuel mixture, like poor fuel injectors, EGR vas, and low compression. It can also be caused by misfires due to a defective spark plug, coil or other problem.

While these are not all of the signs, it’s a great start. Here’s a more detailed list of the most common causes of rough idle:

Índice de Contenido
  1. Rough Idle Causes
    1. 1. Defective PCV Valve
    2. 2. Vacuum Leak
    3. 3. Dirty Fuel Injectors
    4. 4. Carburetor/Throttle body Issues
    5. 5. Poor EGR Valve
    6. 6. Futility in the Ignition Coil
    7. 7. Defective Spark Plugs/Wires
    8. 8. Low Compression
    9. 9. Filter Blockage
    10. 10. Bad Oxygen Sensors

Rough Idle Causes

1. Defective PCV Valve

Pcv Valve

Your car engine’s Positive Crankcase Ventilation takes the unburned gases escaping from the cylinders and moves them from the crankcase, allowing them to go back to the engine for a complete burn. It is subject to a great deal of pressure because it is part of the engine.

The valve may become blocked over time and render it inoperable. The blockage could also lead to the valve becoming brittle. 

You can prevent it from happening by regularly servicing the PCV valve. You might be able clean the valve if it becomes clogged. It must be replaced if it is not clogged. 

RELATED : 7 Signs Your PCV Valve is Bad

2. Vacuum Leak

Car Vacuum Hose Leak

Vacuum hoses are used to fill the engine compartment. They can all wear down at any time. The hoses will crack over time and become more brittle. A leak can cause a low mixture of fuel and air, leading to a rough idle. A combustion fault within one or more cylinders could also cause it to misfire. 

A vacuum leak can also be caused by leaking vacuum supply tank, vacuum brake boosters, and intake manifold gaseskets. You will find that your car runs rough when it is running at high RPMs. 

A vacuum leak should be detected by checking the codes on the computer. The air/fuel mixture is going to be lean and the engine won’t be able to correct it. 

RELATED: 6 Symptoms of a Vacuum Leak & Causes

3. Dirty Fuel Injectors

Fuel Injector Location

A rough idle can be caused by dirty fuel injectors. A sharp drop in fuel economy will be noticed.

When the injectors get restricted, there’s a significant lack of performance, especially during acceleration. An exhaust gas analyzer can diagnose a dirty fuel injector because it creates higher levels of hydrocarbon and carbon monoxide.

This situation can be prevented by using an injector cleaner ingredient regularly. If the injectors have become blocked, or are restricted in any way, an injectable solution must be used. 

The fuel injectors often have a small filter that can be easily replaced if they become blocked.

Reported: 8 Signs that a Fuel Injector is Bad

4. Carburetor/Throttle body Issues


Carburetors are only available for older vehicles that have accumulated a lot of miles. There are enough cars with them to make this a problem.

The exhaust from a carburetor can produce a distinctive black smoke. This is normal and only happens after the vehicle has warmed up.

First, check the choke. Once the car has warmed up, it should be fully open. If the choke is open, there’s likely an internal carburetor issue that requires a rebuild. Sometimes, it’s just the ethanol in gasoline that causes the carburetor to go bad.

The throttle shaft may also be a problem at the carburetor's base. The shaft can eventually wear down, causing a vacuum leak. 

You may need to inspect the throttle body of a car with a more recent engine. This guide is How to Clean Throttle Body (10 Steps DIY)

5. Poor EGR Valve

Egr Valve Engine

It is an essential device for controlling emissions. This valve allows exhaust gases to be injected into the intake manifold with the sole purpose of reducing motor emissions. 

However, this EGR valve isn’t supposed to operate during idle, at wide open throttle or before the engine is warmed up. The engine's performance will be affected if it is running at these speeds. 

When the EGR valve malfunctions, it doesn’t follow the rules. It sticks open, leading to rough idle or worse, even a stalling engine.

The car’s computer should set a code indicating that this component has gone bad. To see if the problem can be resolved, tap it. You might just need to clean the EGR valve. Otherwise, a low-cost replacement is all that’s needed. 

Related: 6 Signs that an EGR valve is not working properly

6. Futility in the Ignition Coil

Ignition Coils E1609781426872

For proper engine performance, the ignition coil is vital. The ignition coil works with spark plugs in order to ignite fuel/air mixture. 

A car with a defective coil will have a rough idle and misfire. It may also experience poor fuel economy, difficulty accelerating and loss of power. It can lead to the car stalling if it gets worse. 

7. Defective Spark Plugs/Wires

Oil On Spark Plugs

Important to the ignition system are spark plugs, wires. These parts can wear down over time especially if there are contaminants in the cylinders. 

This can be avoided by replacing the spark plugs or wires regularly. Because this is considered a maintenance task, you can find the recommended service interval in your owner’s manual. 

8. Low Compression

Compression Test

At idle, low compression is the most obvious in your car's engine. This will be where you are likely to notice it. You can often notice low compression as a “miss” or misfire on idle.

Cars with over 100,000 miles are most likely to suffer from a low compression miss. Low compression usually causes the mishap. It is necessary to perform a compression test in order to identify the source. 

For the solution to the problem the engine needs to be removed from the vehicle. For proper compression, the valves may need to be changed or perhaps the cam shaft lobes have worn. Either way, it’s not a cheap fix.

Low compression occurs less often than with older cars, and has become a rare feature in modern models.

9. Filter Blockage

Dirty Air Filter

Proper operation of the engine is dependent on the air filter. It’s meant to keep the dust, dirt, and other contaminants from getting into the engine. This can cause the engine to have a restricted airflow because the paper element is easily clogged. 

To keep your engine working properly, you should perform this maintenance task regularly. Ideally, you want to choose a high-quality air filter that isn’t easily clogged. For the small expense, it’s worth protecting your engine. 

10. Bad Oxygen Sensors

Oxygen Sensor

Your car's emissions system is dependent on oxygen sensors. These sensors can be found within the exhaust system. They continuously monitor oxygen concentrations. These data are sent to an engine computer where they can be used to maintain the proper mixture of air and fuel.

High temperatures can make oxygen sensors irreparable. These sensors can wear down over time or become contaminated with carbon. The computer may send incorrect information to it, resulting in an inaccurate air/fuel ratio. A rough idle can occur if the ratio is too low. 

The fault will generate a code which can be read using your scanner. You can use a digital multimeter to pinpoint the oxygen sensor that has gone out of control. 

Whatever is causing your engine to idle rough, it’s important to diagnose the issue quickly and repair it. Neglecting poor engine performance can lead to costly and more expensive repairs.

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