On a modern car, a "tune-up" mostly means replacing the spark plugs, inspecting or replacing ignition coils, and replacing the engine air filter, plus checking for codes and other wear. Most modern spark plugs last a long time, often around 60,000 to 100,000 miles depending on the engine, so check your owner's manual. Signs you need one include rough idle, misfires, hesitation, hard starting and worse fuel economy.
What a modern tune-up includes
- Spark plugs replaced to the manufacturer's spec
- Ignition coils inspected; failed ones replaced
- Engine air filter replaced
- Cabin air filter (often, while they're at it)
- Scan for codes and check live data for misfire counts
- Inspect belts, hoses, PCV valve and visible vacuum lines
Old-school tune-ups (adjusting timing, carburetors, points) don't apply to modern fuel-injected engines.
Signs your car needs spark plugs or coils
- Rough or shaky idle
- Misfires: stumbling, jerking, a flashing check engine light
- Hesitation when accelerating
- Hard starting
- Worse fuel economy
- Check engine codes P0300 to P0306 (misfire). See common OBD-II codes
Spark plugs vs. ignition coils
Most modern engines have one coil per cylinder. A misfire on one cylinder could be the plug, the coil or the injector. A good mechanic swaps the suspect coil to another cylinder to see if the misfire follows it, rather than guessing.
Can it be done by a mobile mechanic?
Yes, on most four-cylinder engines and many V6s and V8s. Some V6 engines hide the rear plugs under the intake manifold, which adds labor. Ask for a quote for your specific engine.
What it costs
Broadly $150 to $350 for spark plugs on many four-cylinder engines, more for V6/V8 engines with hard-to-reach plugs or when coils are replaced too. Get a written quote.
Don't skip the rest of the schedule
Spark plugs are one line on your maintenance schedule. Our car maintenance schedule by mileage shows what else comes due around the same time.
Other causes of rough running
If new plugs don't fix it, look at fuel delivery and air leaks. See bad fuel pump symptoms and check engine light.
Frequently asked questions
How often should spark plugs be replaced?
Check your owner's manual. Many modern plugs last 60,000 to 100,000 miles, but some engines call for sooner.
Can bad spark plugs damage my engine?
Severe misfires can overheat and damage the catalytic converter, an expensive part.
Should I replace all the coils if one fails?
Not necessarily. Replacing only the failed one is common, but on high-mileage engines some owners replace them all.
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