There are a variety of signs of bad spark plugs including difficulty with starting an engine, a rough idle and an increased consumption of gas. Other signs include an engine that has a sudden surge when driving and difficulty with acceleration when applying the gas.
Spark plugs work by igniting the gasoline in a car's engine to keep it moving. In order to avoid issues, spark plugs should be cleaned and checked regularly. If the plugs get bad enough, the car will fail to run and start at all. Fortunately, spark plugs can go for approximately 30,000 miles before they need to be replaced.