Car Idles Rough But Drives Smooth

If your car idles rough but drives smooth, the spark plug is probably faulty or you have water in your fuel tank or even a dirty air filter. Yes all these mentioned could make your car rough idle on startup then smooths out later on a high RPM, the question now is how can you tell which is which.

Your car Idles when you switch on the ignition and the engine starts working, that state when you have not engaged the gear and you are not pressing on the throttle, Yes that is when your car is idling. Normally idling is supposed to sound smooth, slow, steady, and continuous but if the opposite happens, then read on to know the causes and how to fix it.

 

Why Does Car Idles Rough But Drives Smooth

 

If your car idles rough but drives smooth, the causes include a clogged air filter, failing spark plugs, leaking air vents, and even a worn engine mount. To fix this problem, all these mentioned parts have to be inspected and then cleaned or replaced if necessary.

 

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Engine parts such as the spark plugs can become dirty over time or in some cases even if your engine is smoking. But this is a simple case as you easily pull out the plugs and have them cleaned and replaced and everything starts working back normally.

Replacing spark plugs every 20,000 miles should prevent this issue from happening to you. The other cause can be fuel injector cleaning additives that were put into the gas tank to clear carbon buildup in the engine or catalytic converter malfunctions that cause raw fuel to enter into the intake manifold and set.

 

 

A dirty air filter could cause rough idle as well. The car just humans also breathe in some air, the air is used during fuel combustion is in the combustion chamber to burn fuel and the fuel has to be clean and meat the fuel to air ration correctly else the carburetor will get flooded.

You might then be wondering if the case is the same if you have a diesel car or truck? Well, yes even though, there is a little difference between a petrol and diesel car, the causes are pretty much the same. So, yes if your diesel car idles rough but drives smooth, the fault is either one of the already mentioned.

 

4 Common Rough Idle Symptoms

 

The symptoms of a rough idling car includes idling below or above its regular speed, inconsistent RPM, shaking or vibration through the car and skipping, slipping sound. One or all of these mentioned an be evidently experiend in a car that is experiencing rough idle.

If your car is new, you definitely might not know how a rough idling car feels like except if you have experienced it before. However, due to usage and age, some of the engine and overall car parts begin to wear off thereby failing to perform their functions appropriately.

 

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Rough idling can be in two forms, either you are idling rough and driving smooth or idling rough all the way. Whatever the case may be, they both share some common causes of rough idles.

 

How to Fix a Rough Idle in Your Car

 

Rough idle typically happens when your engine is cold or has just been started, but could happen at any time. It takes some patience and the right tools to diagnose the problem that may be causing your vehicle to have this issue.

To fix a rough idle, first make sure that your vehicle’s air filter is clean and replace it if necessary. You may also want to check for any leaks in the fuel line, air intake hose, or vacuum hoses. This should help you determine what exactly needs to be fixed if there are no other problems with your engine at all.

 

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If this does not work then you should probably talk visit a professional for a wholistic diagnosis and fix. However, before you spend any money at the mechanics, you should try these simple fixes too.

  • Check if there’s anything blocking the air intake.
  • Make sure that the thermostat is set at an appropriate temperature.
  • Remove any obstructions from around the throttle.
  • Listen for loud noises.

It’s always frustrating when you’re stuck in traffic and your car won’t start up. But this problem is usually minor and easy to solve, so don’t get too worried!

 

What Causes a Car to Idle Up and Down

 

Idling itself is the rate at which the engine operates when it is not driven or engaged in gear. A better picture of an idling car is when you have just started your vehicle in the morning and you are not raving it or when parked to quickly get something but the engine is running.

Below are common causes of why your truck, van, or car could be idling rough. Continue reading to find out

  • Failing spark plugs

A bad spark plug can be very notorious to detect sometimes as it needs very close attention and monitoring to tell if is the spark plug or spark wires. Either the spark plugs or spark cable connected to the spark plug could be the cause of rough idle.

Spark plugs are responsible for igniting sparks in the combustion chamber enough to make the mixed fuel and air burn thereby producing energy. Spark plugs are the usual cause of an idling rough engine.

When enough sparks to ignite the engine are not produced by the spark plugs, fuel mixed with air in the combustion chamber would not burn as expected. When fuel mixed with air is not burnt well, there would no production of enough consistent energy for the engine to run thereby causing a rough idle.

  • Worn engine mount or engine seat

Most likely, this would not apply to new cars, trucks, and vans, as everything is expected to be new. In older vehicles, an engine seat or moto mount could be the reason why your car idles rough but drives smooth.

Engine mounts, also known as motor mounts, are designed to secure your vehicle’s engine and transmission to the subframe. They are also intended to absorb vibration and shock to ensure that the driver is unable to feel any movement of the motor.

Like any vehicle part, however, the engine mounts can go bad. Signs of a bad moto mount include car jerks, unusual vibration, rocky start, and impacted noise.

  • Vacuum Leak

Under the hood are many hoses that snake around the engine. These hoses are meant to create a vacuum seal for the air and fuel controlled by the throttle to regulate airflow and engine speed and vacuum within the intake manifold.                                                                                                                                                                                                  After a few years and exposure to extreme temperatures, the rubber hoses wear down and develop leaks. When too much air is added to the air/fuel mixture it can cause misfires, rough idle, and an increase in RPMs. Have a technician inspect your vehicle’s hoses regularly for cracks, breaks, or dryness and replace them every 50,000 miles.

  • Clogged fuel injectors

Fuel injectors can get clogged or even blocked over time as a result of dirty and tin carbon filings present in the fuel or fuel line. The fuel injector is responsible for delivering fuel to the combustion chamber to aid combustion.

The injector performs its function through specially designed valves that can open and close within a second. The main function of the injector is to deliver fuel to the combustion chamber.

Any of the above-mentioned faulty engine parts can be the reason why your car idles rough but drives smooth. Even though you can do almost nothing to fix rough idles as an average driver or car owner, it is good to have an idea before going to the mechanic.

 

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Will a vacuum leak cause rough idle?

 

If any of these hoses spring a leak, a lean air/fuel condition will result, causing a rough idle from the resulting engine misfire. Vacuum leaks can also be caused by leaking intake manifold gaskets, vacuum brake boosters, or vacuum supply tanks.

 

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After a few years and exposure to extreme temperatures, the rubber hoses wear down and develop leaks. When too much air is added to the air/fuel mixture it can cause misfires, rough idle, and an increase in RPMs. Have a technician inspect your vehicle’s hoses regularly for cracks, breaks, or dryness and replace them every 50,000 miles.

 

What causes a car to shake while idling?

 

 

A worn-out seat engine or motor mount can be a major cause of your car shaking or vibrating when driving. Failing spark plugs are not left out either, this device can be the culprit are very notorious for causing your car to shake sometimes.

When spark plugs are covered by soot they tend to give fewer sparks or lose their ability to spark. If spark plugs lose their sparks they fail to produce enough spark to ignite the fuel mixed with are in the engine.

Worn-out motor mounts are not left out among the cause of shaking vehicles. Engine mounts are the component responsible for securing the engine of a vehicle to the chassis.

If either the motor mount or the spark plugs are faulty, they can easily cause shaking abnormalities. You should consider replacing them as quickly as possible to avoid causing further damage.

 

Can a bad air filter cause rough idle?

 

Can a bad air filter cause rough idle? Yes is the direct answer to this question but let me explain how an air filter works. The air filter is responsible for cleaning the air that is being delivered to the engine.

Funny right? Yes, the engine breaths in the air too just like you do and it breaths in clean air. A dirty air filter reduces the amount of clean air that is getting through to the engine, decreasing its power and performance.

So the bottom line is if your car’s air filter is dirty it will directly impact your engine performance. Symptoms of a bad air filter include reduced horsepower, black, sooty smoke or flames exiting the exhaust, and the smell of gasoline when starting the car.

 

Conclusion

 

A rough idle is an issue that can be caused by a variety of different problems. When you have a rough idle, it can cause your vehicle to not move as quickly as it would ordinarily.

Remember, a failing spark plug or a dirty air filter could be the reason why your car idles rough but drives smooth. If you have any questions please ask us using the comment section below we will be glad to answer.

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