If the engine doesn’t seem to catch right away, that might be your first heads-up. It can also be a sign if the engine hesitates or doesn’t have the same pull from acceleration. Rough idling with engine misfires is another sure sign, along with greater fuel consumption. Any or all of these symptoms suggest it’s time to have your spark plugs changed. Read our Car Advice article How Do I Know If My Spark Plugs Need Replacing? for a full overview including additional signs it’s time to replace.

Spark plugs generally cost less $10 each. The cost depends on the expected life and material used on the electrode. Platinum- or iridium-tipped plugs using laser technology cost the most: as much as $25 each. You can pay between $16 and $100 for a set of spark plugs, depending on the type of plugs you need and the number of cylinders your engine has. And when figuring out the price, it helps to remember that some specialty engines use two spark plugs per cylinder.

In the past, experts recommended changing spark plugs every 30,000 miles or so. With today’s extended-life spark plugs, the life expectancy can go as high as 100,000 miles. Checking and replacing the spark plugs is usually part of your vehicle’s routine service interval. Rarely do you need to make an appointment just for the spark plugs. Consult your Owner’s Manual for more details.

Usually, yes. You should replace the spark plug wires when you get new spark plugs. With standard spark plugs, that might be every 30,000-40,000 miles or so. If your vehicle uses extended-life spark plugs, you could go as long as 100,000 miles before changing the spark plug wires. It’s still a good idea to regularly inspect the wires for any frays, cracks, and even bites (yes, bites!), since some wires are made from a soy-based material that’s a favorite snack for rodents.