Though spark plugs should be changed roughly every 30,000 miles, there are warning signs you should watch out for. Spark plugs connect the ignition coil and combustion chamber. The moment you start your car, the spark plugs transfer the high-voltage current from the ignition coil to the engine's combustion chamber. That being said, if the spark plugs aren't working correctly, you'll notice the following issues:
Slow start or not starting at all
Engine misfires
Engine is running but sounds rough
Idling that sounds rough
Acceleration is poor and sluggish
Fuel consumption is higher than usual
