15 Reasons Why Your Car Is Rough Idling

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rough idling

Idling occurs once you start your car and leave it running without hitting the gas pedal or shifting gears. A good engine can spin at a constant pace of 1,000 RPM (revolutions per minute). During this idle speed, your engine can supply enough power to run your vehicle’s entire systems, such as power steering, cooling systems, and electrical systems. Idling at a constant engine speed is smooth and silent.

Whenever an automobile is experiencing a rough idle, your car shakes, vibrates obnoxiously, and makes strange sounds. Its tachometer pointer will also move about instead of keeping at a constant RPM; the tachometer’s purpose is to measure a car’s RPM.

Although a car idling roughly may appear to be a minor issue, it’s a warning that something in your engine isn’t operating properly. Rough idling may cause poor fuel economy, starting difficulties, and severe engine issues over time.

In this article, we’ll be discussing what causes a rough idle and offer some tips on how to fix it. Keep reading to learn more!

Rough Idling Causes

A rough idling engine is an indication that something more serious is occurring with your engine. An issue frequently causes it with the mechanism that maintains the proper combination of fuel and air within your engine. Rough idling is challenging to identify since various factors may cause it. Below are the common causes why your car is suffering from rough idle.

Vacuum Leaks

Vacuum hoses are almost everywhere in your engine bay, any of which could fail at any time. Such hoses get brittle and shatter over time. Whenever one develops a leak, it results in a lean air/fuel mixture, resulting in a rough idle. Due to a significant combustion problem in one or more engine cylinders, it could also trigger your engine to misfire.

A leak in brake boosters, supply tanks, and intake manifold gaskets could cause vacuum system leaks. While driving a vehicle suffering a vacuum leak, you’ll notice that everything works perfectly when both RPMs or speed are increased, but it makes your vehicle idle rough.

Any vacuum leak must be detected by inspecting the computer’s codes. The air/fuel mixture would be lean, and your engine has no way of correcting it.

Bad PCV Valve

The Positive Crankcase Ventilation of your engine removes unburned gases off its cylinders. It transports them out of the crankcase, enabling them to return to your engine for a thorough burn. Since your PCV valve is used in the engine, it is subjected to a great deal of stress and is frequently clogged with pollutants like sludge or dirt.

The PCV valve might get clogged over time, making it ineffective. This obstruction could also cause a leak, causing its air/fuel mixture to get lean and causing a rough idle.

Dirty Fuel Injector

A rough idle is among the issues you’ll encounter if your fuel injectors get dirty. You’ll also notice a significant drop in fuel efficiency.

There is a considerable loss of power whenever your fuel injector is blocked, particularly during acceleration. The exhaust gas sensor can detect filthy fuel injectors since clogged injectors provide more significant carbon and hydrocarbon monoxide measurements.

Dirty fuel injectors can be prevented by applying an injector cleaning additive regularly. An injectable fluid would require to be put into the system if the injectors become restricted or clogged.

Faulty EGR Valve

An important emission control device is called Exhaust Gas Recirculation Valve. It permits exhaust gas to reach your intake manifold for the primary objective of lowering the engine’s emissions. On the other hand, the EGR valves should not be utilized at idle, wide-open throttle or before your vehicle’s engine has warmed up.

Your engine’s performance will be harmed if it operates during any of these periods. Once your EGR valve fails, it does not operate according to the requirements. Instead, it stays open, resulting in a rough idle or, worse, a stalled engine.

A code must be set in your car’s computer stating that a particular component has failed. You could also press it to check if you can get it out of its stuck condition. Cleaning the clogged EGR valve could be enough to fix the problem. Otherwise, a low-cost alternative will suffice.

Defective Ignition Coils

Ensuring your engine’s optimal performance necessitates the utilization of an ignition coil. The ignition system ignites the fuel/air ratio in tandem with your spark plugs. If the coil is damaged, your automobile could have a rough idle, power loss, a misfiring engine, poor acceleration, and reduced fuel economy. As the issue grows more serious, your car may stall.

Carburetor/Throttle body Issues

Carburetors are only found in older automobiles with a lot of mileage. However, there are plenty of them to be an issue. Carburetor problems cause the exhaust to emit a distinctive black smoke. Typically, this smoke appears after the car has fully warmed up. The choke should be checked first. Once your vehicle has warmed up, it must be entirely open.

When the choke is opened, there’s probably a problem with the carburetor that needs a rebuild. The ethanol in petrol can sometimes trigger the carburetor to malfunction. However, an issue with its throttle shaft at your carburetor base is also possible. This may eventually wear down, resulting in a vacuum leak.

Low Compression

Engine low compression is most apparent at idle and would consequently be the first thing you observe. Low compression is typically seen as a misfire while the engine is idling roughly. Cars with greater than 100,000 mileage are the most likely to suffer from a misfire caused by low compression.

The misfire usually happens when one of your cylinders’ compression is too low. A compression test must be done to identify whether this is the reason. Your engine would require to be dismantled and repaired to remedy the issue.

The valves would need to be replaced for optimal compression, or even camshaft lobes could be worn out. In any case, it isn’t an affordable remedy. Low compression doesn’t occur as frequently in contemporary automobiles as in older vehicles, and it is becoming more uncommon.

Bad Fuel Pump

At normal idling, when your fuel pump is defective or otherwise not in good working condition, you might not have enough fuel being pumped into the combustion chamber. This might result in a loud boom accompanied by a lesser bang that you’ll hear as a popping or sputtering noise through your floorboard.

Faulty Oxygen Sensor

The oxygen sensor (O2 sensor) is a tiny sensitive component generally attached to the exhaust system. A defective oxygen sensor might also cause your check engine light to illuminate (steady or flashing) or a rough idling car.

Head Gasket Leak

It could be an extremely costly and frustrating experience if the head gasket leaks. This is because going to your head gasket is a hassle, yet the seal it creates is crucial for proper combustion and the life of your engine.

If you notice white smoke streaming from your exhaust after your vehicle has warmed up, you probably have a head gasket leak or a blown head gasket. Additionally, when the coolant is leaking, seems milky or frothy, or has to refill often, you most likely have a leaking head gasket.

Dirty or Clogged Air Filter

If your engine’s air filter is dirty, particles will begin to appear in the air entering your engine throughout the combustion cycle. Either that or the dirt in your air filter will prevent the air needed to perform the combustion cycle at the configured level from entering the system. This might cause a misfire or a rough idle as a consequence.

Faulty Spark Plugs/Wires

Your idling may fluctuate while you’re car is on stationary if one of its spark plugs isn’t firing in the proper sequence or isn’t sparking in any way. One of the most critical aspects of combustion is the spark, which is required to get your engine operating.

If three out of four spark plugs in your four-cylinder engine fire in the proper sequence, you’ll hear three bangs followed by stillness.  When you’re stopped at a stoplight or starting your vehicle in the morning, you’ll undoubtedly feel this.

Whenever your automobile is idling weirdly, inspect the spark plugs and spark plug wires and replace them if they’re damaged or otherwise unclean.

Malfunctioning Oxygen Sensors

These oxygen sensors are critical components of your vehicle’s emissions system. They’re in your exhaust system, continually checking for oxygen levels in the exhaust gases. The data is relayed into the engine computer, which uses it to keep the air/fuel ratio correct.

On the other hand, Oxygen sensors degrade with time as a result of the high temperatures they are exposed to. They wear down or get contaminated with carbon deposits over time. When this occurs, the computer receives incorrect data such as too much air or fuel, resulting in a wrong air/fuel ratio. A rough idle happens when the mixture gets too lean.

Bad Idle Air Control

To manage engine idle speed, your air idle control (IAC) controls the quantity of air accessing your engine. Carbon deposits on your IAC valve or threads eventually obstruct air passage into the engine. This simulates a vacuum leak and a rough idle, or even worse, leading your car’s engine to stop while idling.

Idle Speed Needs Adjustments

Your automobile idles at a fixed pace, which an automotive technician may modify with relative ease. Idling speed is a straightforward concept: it’s the rate at which your engine rotates while the automobile is still. If its speed is too sluggish, it’s like having a slow pulse — engine oil pressure decreases and can’t circulate properly, causing the rough idling of your vehicle.

How to Fix Rough Idling

Engines must be silent and smooth to operate. If your automobile is making strange sounds, stalling out when accelerating, or vibrating and trembling while idling, you must take it to a reputable repair shop. If some codes were triggered, the technician would inspect your engine computer.

The technician will address and correct the faults that create your rough idle once they have been found. If your engine codes fail to identify why your car is idling rough, the technician will look into the most likely reasons and ensure everything is in functioning order.

While several difficulties might induce rough idling, most of them are caused by damage, dirt accumulation, or wear and tear. Getting your engine well-maintained can go a long way toward minimizing problems that might result in vehicle damage.

Filter and fluid replacements, tune-ups, and scheduled maintenance should be done regularly. It can help you spot problems early on when they’re more straightforward and less costly to repair.

Other Rough Idle Causes

If the causes mentioned above fail to address the issue, try these. There’s got to be a problem with these components below; this is a rare cause but could also be the reason.


It’s also critical to take your car to a mechanic when you discover anything isn’t working correctly. Schedule an appointment if you notice a drop in your vehicle’s performance, hear strange sounds, feel unusual sensations when seated behind the wheel such as rough idling, or see its check engine light come on. It could be tempting to put off car maintenance, but you’ll wind up paying more money in the long run.

Nobody likes to be in a vehicle that breaks down unexpectedly. If your automobile is idling roughly, don’t disregard the problem. It would be quickly addressed if you handled it asap.


What can cause a rough idle at low rpm?

The reasons for a rough idle at low rpm can be caused by a multitude of difficulties, including dirty fuel injectors, blocked air filters, faulty spark plugs, and a range of exhaust system problems.

What does rough idle feel like?

You’ll most likely notice when your car is idling roughly right away. A rough idle is commonly identified by an increased trembling and vibrating feeling in your car; however, some examples are less harsh than others. You can also hear strange noises and see erratic RPM readings.

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