There are a variety of problems that crop up when spark plugs need to be replaced. Some of the symptoms include difficulty starting, lack of acceleration, rough idle and increased fuel consumption. In general, spark plugs that need to be replaced cause a variety of poor performance symptoms in a car. Many of these symptoms have other causes, but together they can indicate bad spark plugs.
Spark plugs can be a reason for a car not starting, as lack of spark is one of the two reasons for a car not to start. It can also be the reason behind unusual battery drain. Misfiring cylinders are another symptom of faulty spark plugs. A misfire causes the car to jerk briefly and then continue its normal operation. Similarly, this symptom could be due to the engine surging, which is another sign of faulty spark plugs.
If a car suddenly seems to be consuming way more fuel than usual, the spark plugs could be the culprit. This is due to incomplete combustion because of the inadequate spark. Fuel consumption can go up by as much as 30 percent in these cases. Similarly, the vehicle might feel sluggish and hesitate or lurch upon acceleration.