7 Bad Spark Plug Symptoms Arizona Drivers Should Never Ignore
Reviewed by Eric Shepherd, ASE-Certified Technician
Did you know that spark plugs are one of the most overlooked engine maintenance items on modern vehicles? Spark plugs play a crucial role each time you turn on your car and as you are driving. Once they start to wear out, the symptoms can gradually turn into large performance issues. For Arizona drivers, what began as a rough idle might turn into reduced fuel economy and engine misfires quickly, along with costly repairs.
The extreme desert heat can make any issues worse. During the summer months the under-hood temperatures skyrocket while cars spend all day baking in work parking lots only to continue to cook on long commutes home on Valley freeways with the air conditioning blasting. All these conditions contribute to additional stress on your vehicle's ignition system and magnify existing spark plug issues. Most drivers don't think about spark plugs until their car starts acting differently. The challenge is that spark plug problems often develop so gradually that it's easy to blame bad fuel, Arizona heat, or an aging vehicle instead.
Bad Spark Plug Symptoms at a Glance
The most common signs of bad spark plugs include:
- Engine misfires
- Rough idle
- Hard starting
- Poor fuel economy
- Sluggish acceleration
- Engine vibration
- Check Engine Light
If you're experiencing one or more of these symptoms, schedule an inspection before ignition problems become more expensive.
What Are Spark Plugs?
In gasoline engines, spark plugs are small devices that create a spark that starts the combustion process inside of the engine. For example, if your engine was a campfire, the air and fuel would be the firewood, and the spark plug would be the match. The combustion creates the power that allows your vehicle to move. Every cylinder in your engine has one. When you press on the gas, the ignition system sends electricity to the spark plug which ignites the compressed air-fuel mixture inside the cylinder.
The Difference Between Spark Plugs and Glow Plugs
Where spark plugs are "the match" that ignites the air-fuel mixture in a gasoline engine, glow plugs work more like a space heater in a diesel engine. Rather than using a spark, diesel engines compress air so tightly that it becomes extremely hot. The fuel is injected into that hot air and ignites on its own. When a diesel engine is cold the air may not get hot enough in the cylinders and that's where glow plugs come in – they act as tiny space heaters, heating up the combustion chamber. Where spark plugs act as a match to light a campfire, glow plugs are like preheating the wood until it's hot enough to catch fire on its own.
Glow Plug Fun Fact
Many modern diesel engines in Arizona may barely use their glow plugs during a hot Phoenix summer day because ambient temperatures are already so high. However, the glow plugs are still important for reliable starts, emissions control, and smooth cold-engine operation.
What Do Spark Plugs Do?
Spark plugs play a vital role in your engine by igniting the air-fuel mixture. The controlled combustion is what creates the power needed to actually move your vehicle down the road. Spark plugs support:
- Efficient fuel combustion
- Smooth engine operation
- Proper engine performance
- Lower emissions
- Reliable starting
- Better fuel economy
Like many other components on your vehicle, spark plugs are a wearable maintenance item that wasn't designed to last forever. As the plug wears, deposits can build up gradually, reducing spark quality and causing problems that cost far more than replacing a set of spark plugs on time. Modern engines were designed to operate on precise combustion timing, so even just one worn spark plug on your V-8 can make a difference and on smaller displacement engines with fewer cylinders the symptoms of one bad plug can be even more noticeable.
What Are the Symptoms of Bad Spark Plugs?
You will know you have bad spark plugs when the engine starts to misfire, you experience a rough idle, your car has a hard time starting and your fuel economy starts to become really bad. Other signs could be reduced engine performance like sluggish acceleration when taking off from a light, or increased engine vibrations or even a check engine light.
Because several engine problems can create similar symptoms, technicians typically confirm spark plug issues by scanning diagnostic trouble codes, inspecting the spark plugs themselves, evaluating ignition coil performance, and checking for fuel or air delivery problems before recommending repairs.
Engine Misfires
One of the most common symptoms that your spark plugs are going bad is an engine misfire. You might notice your vehicle hesitating while climbing up the mountains on your way to Flagstaff, accelerating to get up to speed on the 303 or when passing someone on the 101.
A misfire is when one cylinder fails to ignite the air-fuel mixture. Rather than producing power, it doesn't contribute to the combustion cycle. As the spark plug gets worse and continues to deteriorate, the misfires become more frequent.
Arizona drivers often notice misfires as:
- Sudden hesitation
- Jerking during acceleration
- Intermittent stumbling
- Loss of power
- Rough engine operation
Since misfires are one of the earliest signs of bad spark plugs, addressing them early can help prevent damage to other ignition or emission components.
Rough Idle
When you're sitting at a stop light and it seems like your car is about to stall out or is running unusually rough, it could be a sign that your spark plugs are failing. When the spark plugs aren't igniting the air-fuel mixture consistently, the engine can start to struggle to maintain smooth operation.
Most drivers will notice:
- Increased vibration
- Shaking while stopped
- Uneven engine speed
- Engine stumbling at idle
You will notice these symptoms the most when you're hitting one stoplight after the next along Bell Road in Phoenix or Bell Road through Surprise and Sun City West.
Difficulty Starting the Engine
Spark plugs play a direct role when starting your vehicle's engine. When functioning properly, the spark plugs generate enough energy to ignite the air-fuel mixture quickly. If the plugs are worn, you may experience longer crank times or delayed engine startup. Sometimes these issues can be intermittent and occasionally the vehicle may not start.
Few things are more frustrating than turning the key after a long Arizona workday and wondering whether your vehicle will start. Hours of sitting in triple-digit heat can expose existing ignition system problems that may have gone unnoticed in cooler conditions.
Poor Fuel Economy
Over time, as spark plugs lose efficiency, your fuel economy is reduced as well because the combustion has become less efficient. This means your engine is working harder to produce the same power it needs when it has optimal combustion.
This can result in:
- Increased fuel consumption
- More frequent trips to the gas station
- Reduced miles per gallon
The decline is gradual, so it's easy to overlook. Most Phoenix drivers have a fairly normal routine. Whether you commute through Phoenix, Mesa, Chandler, Tempe or Scottsdale, gradually increasing fuel costs can sometimes point to worn spark plugs.
Sluggish Acceleration
In addition to the slow start ups, the rough idles, the increased gas consumption, you might notice that your car doesn't seem as peppy as it once was getting on the freeway. At Gemba Automotive, we hear drivers commonly describe the symptoms as:
- Slow throttle response
- Reduced engine power
- Hesitation during acceleration
- Lack of passing power
- Overall sluggishness
Acceleration issues can also be caused by other things such as fuel delivery (injectors, fuel pumps, etc.) or other ignition system components. It is important to have your vehicle inspected to determine if spark plugs are the root cause of the sluggish performance before replacing any parts.
Increased Engine Vibration
As the spark plugs continue to deteriorate, you will start to notice engine vibrations. It can be easy to confuse this with bad engine mounts, a tire issue or suspension component. When one or more of the engine's cylinders isn't firing as it should, the balance of the engine is disrupted which can lead to vibrations felt in the steering wheel, the floorboard, the seats, and throughout the vehicle body.
The vibrations will start to become noticed only under certain circumstances, like stopped at a traffic light. Then, over time as the issue becomes worse, they will become more frequent and more pronounced.
Check Engine Light
Modern vehicles have sensors all over the place and are constantly monitoring the engine and various systems. If the computer in your vehicle detects a combustion problem, it will illuminate the check engine light and store a code that can be used to better determine the cause of the light.
Spark plug issues commonly trigger:
- Misfire codes
- Cylinder-specific fault codes
- Ignition system codes
- Performance-related diagnostic codes
It is important to note that the engine is complex, and the check engine light can mean many things. Issues with fuel injectors, ignition coils, other sensors, vacuum leaks and emissions systems can all produce similar warnings.
Can You Drive With Bad Spark Plugs?
You might be thinking, none of these symptoms seem so bad, maybe I can drive for a while. While your vehicle will likely remain operational, ignoring the symptoms of bad spark plugs can lead to expensive repairs down the road in addition to increased fuel consumption, which means many more trips to the gas station than you would normally make.
For example, as your spark plugs wear down, the ignition coils often work harder to produce the voltage needed. This can shorten the life of the coil and lead to ignition coil failure. Spark plugs often wear out naturally, while ignition coils deliver the electrical voltage that allows the plugs to fire. Either component can produce similar symptoms, which is why proper diagnosis is important.
Another expensive consequence of neglected spark plugs is catalytic converter damage. Constant misfires allow unburned fuel to enter the exhaust system. When the fuel reaches the catalytic converter, it can cause severe internal damage. Rather than relying on generalized mileage estimates, Arizona drivers should follow the manufacturer's recommended maintenance schedule for their specific vehicle. If unsure, have your vehicle inspected and a technician will be able to help identify if you are experiencing any issues due to spark plugs.
When Should You Replace Spark Plugs?
Knowing when to replace your spark plugs depends on your vehicle and the type of spark plug you have. Spark plugs come in three basic varieties: copper, platinum, and Iridium. Both Platinum and Iridium also come in a "double" variant.
Spark Plug Comparison
| Spark Plug Type | Typical Replacement Interval |
|---|---|
| Copper | 20,000 – 30,000 miles |
| Platinum | 60,000 – 100,000 miles |
| Iridium | 80,000 – 120,000 miles |
To be safe, always follow your manufacturer's maintenance schedule.
Copper Spark Plugs
Despite the name, copper spark plugs feature nickel alloy with a copper core. They have excellent conductivity and are most commonly used in older vehicles, but generally have shorter service life.
Platinum Plugs
Platinum spark plugs use a platinum disc on the center of the electrode. They were designed for improved durability and longer service intervals compared to copper plugs but are more expensive. Double platinum spark plugs have platinum on both the center and ground electrodes.
Iridium Plugs
Iridium is one of the hardest and most durable metals used in spark plugs. These types of spark plugs are most used in modern vehicles and typically offer the longest service life. They have a strong, consistent spark and are the most resistant to heat and wear.
How Arizona Heat Makes Bad Spark Plug Symptoms Worse
Arizona's infamous triple-digit heat is known for creating some of the harshest operating conditions for vehicles. When the temperature pushes past 110 degrees, the engine components endure more stress and if there is an existing ignition problem, it will be magnified and become more noticeable during an Arizona summer.
When to Schedule a Spark Plug Inspection
If you've noticed any of the following symptoms above, it's a good idea to have your vehicle inspected.
- A check engine light
- Rough idle
- Engine misfires
- Reduced fuel economy
- Hard starting
- Sluggish acceleration
- Increased engine vibration
At Gemba Automotive, our ASE-Certified Technicians help Arizona drivers diagnose performance concerns, identify bad spark plug symptoms and recommend maintenance solutions that keep vehicles running reliably in the demanding desert climate. If your vehicle isn't performing the way it should, scheduling an inspection now can help prevent larger repairs later.
Frequently Asked Questions
What are the symptoms of bad spark plugs?
Misfires, rough idling, poor fuel economy, slow starts, engine vibration and check engine lights are all signs of bad spark plugs that shouldn't be ignored.
Can bad spark plugs cause a check engine light?
Engine misfires due to spark plugs can often trigger a check engine light.
How long do spark plugs last?
Manufacturer recommendations should always be followed, as the lifespan of a spark plug can vary by vehicle and plug type. Most modern spark plugs last significantly longer than older designs.
Can bad spark plugs reduce fuel economy?
Worn spark plugs can create incomplete combustion, causing the engine to burn more fuel.
What happens if you don't replace spark plugs?
Ignoring worn spark plugs can lead to ignition coil damage, catalytic converter failure, reduced performance and higher repair costs.
Can Arizona heat affect spark plug performance?
Extreme heat can increase stress on ignition components and may worsen existing spark plug issues.
Can bad spark plugs cause your car to shake?
Yes. Worn spark plugs can cause engine misfires that lead to shaking or vibration, especially while idling or accelerating. Other issues can cause similar symptoms, so a proper inspection is recommended.
Can bad spark plugs damage the engine?
While worn spark plugs don't usually damage the engine directly, they can lead to ignition coil failure, catalytic converter damage, reduced performance, and higher repair costs if left unaddressed.
Can bad spark plugs cause poor acceleration?
Yes. Worn spark plugs can cause hesitation, sluggish acceleration, and reduced engine power because the air-fuel mixture isn't igniting efficiently.
How much does it cost to replace spark plugs?
Spark plug replacement costs vary depending on your vehicle, the type of spark plugs it uses, and the labor required. A professional inspection can provide an accurate estimate for your specific vehicle.