Engine compression and the ignition system are also very important to overall driveability and performance. Always verify that the ignition system is in good condition and functioning properly before troubleshooting the fuel injection system. See IGNITION. On older engines with high mileage, worn engine components and poor compression may be a factor in poor performance. For more information on engine problems and engine troubleshooting, including compression testing, see ENGINE. Do not try to correct engine trouble by making simple adjustments to the idle speed or the idle mixture (CO). Changing these settings without the proper measuring equipment will only be a hindrance when trying to locate the real fault.