Car Maintenance And Repairs

Car Idles Rough But Drives Smooth- What Happen And What To Do?

Mike Cross
Updated Oct 17, 2020
Car Idles Rough But Drives Smooth

Cars are complex machines. For the most part, they are easy to maintain and do not have major issues. However, sometimes a problem can arise. One such issue is when the car idles a bit roughly, but then seems to drive smoothly.

Anytime there may be an issue with your engine, it is crucial to have it diagnosed and repaired as soon as possible. We rely on our cars and trucks every day.  The longer you let a problem go, there bigger the risk to your car both mechanically and financially. Vehicle engine problems are not fun, but they need to be addressed head on.

Car Idles Rough But Drives Smooth
Car Idles Rough But Drives Smooth

What is engine idling?

When your car or vehicle is on, but not driving, it is considered to be in idle. This happens when you are at a stop light, waiting for people to get in your car or even just waiting for your car to warm-up first thing in the morning.

When your car is in idle, it should be smooth sounding and you should not feel any motion.

What is rough idling?

If you have your car in idle, and feel or hear anything, that is considered rough idle. It can be a sputtering sound; it can be a knocking sound, or it can feel like your car is shaking. These are signs that your car is idling rough. You need to figure out why this is happening before any further damage can happen to your vehicle.

Even if the rough idling stops after a few minutes and your car drives smoothly, you still need to get to the root cause of the rough idle. It is not normal for a car to experience rough idling.

How can you figure out why your car is rough idling?

Your car can be experiencing rough idling due to a few different causes. You will need to figure out why. One way to find out why is to use a diagnostic tool. These scanners can be purchased and used at home with software downloaded to your computer or an app on your phone.

Generally speaking, there are a few different causes of rough idling.

1.Vacuum Leak

With all the hoses that are included under the hood, a vacuum leak can be the cause of some rough idling. These hoses are needed for both fuel and air. Older engines that have a carburetor use a vacuum to pull fuel into the engine.

Newer engines have a throttle which regulates airflow, and this creates a vacuum through the manifold. Over time it is very possible that the hoses become worn out and develop a leak. When this happens too much air will get mixed in with the fuel and it will cause some rough idling.

2.Spark Plugs and Wires

If your car has spark plugs or spark plug wires that are damaged or worn out, rough idling can occur. Spark plugs take the electrical current from the ignition coils and use it to ignite the air and fuel mixture in the combustion chamber. If the spark plug is worn, damaged or not installed correctly, it can cause the fuel to be burned inconsistently.

This should be addressed immediately, because if the spark plugs are not replaced you will eventually have trouble while driving.

3.Dirty Fuel Injector

Dirty fuel injector engine
Dirty fuel injector engine

If your fuel injector is dirty, that could also be a cause of rough idling. The fuel injector in your car dispenses fuel into the engine. This is designed to dispense fuel at an exact angle and quantity to ensure optimal performance of your engine. Over time the fuel injector can experience some buildup. This is a relatively easy issue to fix. Simply add an injection cleaner to your fuel.

A dirty fuel injector can also cause your vehicle to get poor gas mileage.

4.Check your carburetor

If you have an older vehicle, chances are that it uses a carburetor.

Look at the exhaust smoke; if it comes out black, that is an indication that there is an issue with the carburetor. Sometimes this is because there is a buildup of deposits in the system.

Again, you can add a carburetor cleaner to the system which will help clear away deposits and keep the system running smoothly.

What should you do next?

As soon as you notice your car idling rough, even if it is only for the first few minutes, you should find out why. If you have the best obd2 scanner at home, you can plug it in and check yourself. If not, take your car into your mechanic and have him check it out.

Definitely change or repair what is worn out. Spark plugs and their wires should be replaced. It is easy enough to add fuel injector cleaner or carburetor cleaner to your vehicle’s system. And all hoses should be functioning properly.

If you are handy with tools and comfortable working with cars, these steps should be easy to do. All of the needed parts can be found at your local auto parts store.

Should I use brand name parts?

Most people feel that there is a benefit to using brand name parts on your car. This is because well known brand names have proven themselves to customers. In addition, they are also likely to stand behind their products.

What else should I check?

In addition to the areas listed above, it makes good sense to check other parts as well. Check that all valves and coils are in good shape and not loose. Replace any dirty filters you see. Make sure bolts are appropriately tightened. If you are under the hood, it is a good time to double check.


Your car should start smoothly, idle smoothly and drive smoothly. Any sign of rough idling is a sign that things need to be checked. Rough idling should be considered an early warning sign. Heed it wisely. Taking care of a problem while still small, will prevent a bigger problem further down the road.

Mike Cross
Life is too short to drive with stock audio

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One comment on “Car Idles Rough But Drives Smooth- What Happen And What To Do?”

  1. My car is 2006 GMC envoy well it dosent act up all the time but it does act up when at a complete stop or as I am stopping it starts to spit an sputter like it wants to cut off. It never cuts off though the engine light will flash briefly then stay on is it my fuel pump what could it be?

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