When Should You Replace Spark Plugs and Ignition Coils?

The short answer

Replace spark plugs at the manufacturer interval — usually 60,000–100,000 miles for iridium plugs — or sooner if you have a rough idle, misfires, or poor fuel economy. Ignition coils are replaced when they fail testing, not on a schedule.

Intervals, symptoms, and how to avoid catalytic converter damage.

From My Mechanic Pros Texas · 10+ years repairing Texas vehicles

Equipped mobile repair van for on-site vehicle maintenance — Illustrative image for this repair topic; not a customer job photo.

Engine & Diagnostics: key checks

Plug intervals

Copper: ~30,000 miles.

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Coil failure signs

Misfire codes on one cylinder, shaking at idle, and a flashing check engine light under load.

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Why not wait

Misfires send raw fuel into the exhaust and can ruin the catalytic converter.

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Illustrative repair images; not customer job photos.

Plug intervals

Copper: ~30,000 miles. Platinum: ~60,000. Iridium: 60,000–100,000+.

Coil failure signs

Misfire codes on one cylinder, shaking at idle, and a flashing check engine light under load.

Why not wait

Misfires send raw fuel into the exhaust and can ruin the catalytic converter.

Frequently asked questions

Should I replace all coils?

Not necessarily — test first.

Does a tune-up include plugs?

Yes, ours does when due.

How long does it take?

1–3 hours on most engines.

Related services

Mobile tune-ups & maintenance — Spark plugs, filters, belts, and scheduled maintenance.
Mobile spark plug & ignition coil replacement — Misfire repair, spark plugs, coils, and plug wires.