* If one coil is failing: Replacing only the faulty coil is usually the best approach. While coils can fail independently, it's *possible* that age and wear are affecting all of them. However, replacing all coils unnecessarily is costly. Get the failing coil diagnosed and replaced first. Monitor the vehicle afterward for any further misfires.
* If multiple coils are failing (or showing signs of imminent failure): This increases the likelihood that the remaining coils are also nearing the end of their lifespan. Replacing them all might be a preventative measure to avoid repeated repairs and potential further damage to the engine (from misfires). Weigh the cost of replacing them all versus the potential cost and inconvenience of repeated repairs.
* If the car is high mileage and coils are original: The coils in your 2001 LS are likely quite old. Considering preventive maintenance might be worthwhile, especially if you plan to keep the car for a while longer.
* Signs of failing coils: Misfires (rough idle, engine hesitation, check engine light), lack of power, poor fuel economy. A mechanic can use diagnostic tools to pinpoint which coil(s) are at fault.
In short: Start with diagnosing the problem. If only one coil is bad, replace only that one. If multiple coils are failing or the car is very high mileage, consider replacing all of them proactively, but get a qualified mechanic's opinion first to weigh the costs and benefits.
