Idling is what occurs when you start your engine and let it run without pressing the gas or changing gears. When everything is working properly, your idling engine should maintain a steady rate of around 1,000 revolutions per minute, or RPM. This rate allows your engine to power your vehicle’s basic systems, including electrical and cooling systems as well as power steering. A normal idle should be smooth and quiet.
A rough idle, on the other hand, is characterized by bouncing, shaking, and odd noises. The tachometer may jump around instead of staying at a steady RPM. While a rough idle may seem like just a minor annoyance, it’s actually an indicator that there’s something wrong in your engine. If left unresolved, a rough engine idle can lead to poor gas milage, starting issues, and even major engine problems. So, what are some of the most common causes of a rough idle, and how can you fix them?
1. Damaged Spark Plugs and Wires
Spark plugs receive electricity from the ignition coils and use that electricity to ignite the air and fuel mixture inside the engine’s combustion chamber. When a spark plug or spark plug wires become damaged, they can cause the fuel to burn at an inconsistent rate. This creates an imbalance in the mixture, which can lead to rough idling. If the damage is bad enough, your engine may also run roughly while driving. Pay close attention to any jerks or stutters, especially when accelerating, as this is another symptom of bad spark plug damage.
Diesel engines do not have spark plugs, but burned out or damaged glow plugs can have the same effect and cause a rough idle, too.
2. Dirty Fuel Injectors
Fuel injectors let fuel into your engine at a precise angle and rate. This precision ensures optimal engine performance. When the fuel injector gets dirty from buildup or debris, the flow of fuel is restricted. This can lead to an imbalance in the levels of air and fuel in the engine, which will result in rough idling. You will also notice a significant drop in fuel economy, especially when accelerating, when your fuel injectors are dirty.
3. Vacuum Leak
Your vehicle uses a labyrinth of hoses to create a vacuum for the fuel and air to flow throughout the engine. Over time, these hoses can wear out and develop leaks. A vacuum leak can let in too much air, which, when mixed with the fuel, will lead to engine misfiring. This will cause your vehicle to have a rough engine idle, typically with a higher-than-normal RPM.
4. Clogged Air Filter
Just like a dirty fuel injector reduces the flow of fuel, a clogged air filter reduces airflow in your engine. The air filter keeps dust, dirt, and other contaminants out of your engine. When it gets clogged with debris, enough air can’t flow through it into the engine. This will cause a rough idle as well as reduced fuel economy. That’s why it’s important to replace your air filter as part of your regular vehicle maintenance routine. Most vehicle manufacturers recommend replacing air filters each year.
5. Carburetor Problems
Older vehicles have carburetors instead of fuel injectors. A problem with the carburetor will cause rough idling. If you have an older vehicle and you see black smoke coming from your exhaust, then the carburetor going bad is almost certainly the culprit of your vehicle’s rough idle. For vehicles manufactured after the early 1990s, this is not something you need to worry about since modern cars no longer have carburetors.
How to Diagnose Rough Idle Causes
Modern vehicles make it easier to diagnose the cause of a rough idle because they have engine computers that keep track of the fuel, combustion, and exhaust systems within your engine. When something goes wrong, the computer receives a malfunction code, which instructs it to turn on the check engine light on your dashboard. A mechanic can use a code reader to find out what the specific problem is and then determine if that problem is the cause of your vehicle’s rough idle. If the engine computer doesn’t identify an issue, then a mechanic will need to do a further investigation to diagnose the rough idle cause.
Rough Idling in Vehicles with High Mileage
If you’ve ruled out these common rough idle causes and your vehicle has over 100,000 miles on it, then you may have a more serious issue on your hands. A rough idle in a high-mileage vehicle can mean a compression issue from engine wear. A compression test of your engine’s cylinders can be performed by a mechanic to check for this problem. The rough idle can also be caused by other major components wearing down or failing.
Fixing a Rough Idle
Because there are many possible causes of a rough idle, there are also many possible solutions. How to fix a rough idle depends on what’s causing it. Some solutions are straightforward and can be done on your own, such as replacing a clogged air filter or using an injector cleaner gas additive to clean dirty fuel injectors.
Other problems, however, will require the help of an experienced mechanic. An auto or diesel mechanic will be able to figure out what the problem is and provide the right solution to fix it, whether it’s a vacuum leak, damaged spark plug or glow plug, clogged air filter or fuel injector, malfunctioning carburetor, or something else not mentioned above.
Get Your Vehicle Checked by an Expert Knoxville Mechanic
If your vehicle has a rough idle, don’t wait to get it checked out! A rough idle can be a sign of a serious problem in your engine, so you should bring your car in to get it looked at as soon as possible to avoid further damage. Here at Certified Diesel Solutions, our ASE-certified mechanics will go through all the potential rough idle causes and rule each one out until we find your vehicle’s problem. After diagnosing the problem, we will provide you with the best solution so that it won’t cause you any more headaches. Our goal is to get you back on the road as quickly as possible in a vehicle that will safely and reliably get you where you need to go. To schedule vehicle repair or maintenance with the best diesel and auto mechanics in Knoxville, TN, give us a call at 865-964-6598 or fill out our online form. We’ll have your vehicle back in proper working order in no time!