Computerized Engine Tune-up Replacing spark plugs, ignition rotor, and distributor cap if necessary every 24,000 miles will help improve gas mileage and keep your car running smoothly for many more miles. If your Engine is running rough or stalling, the maintenance tune up alone may not cure the problem. Computer controlled Engines have many sensors, switches and solenoids that control Engine functions. Further testing and repairs may be required to cure poor performing Engines.