2005 Saab 9-3 Owner's Manual - Page 152

150 Starting and driving 2 Stopping the engine • Do not rev the engine immediately before switching it off - stop the engine when it is idling. 3 Regulating the boost pressure • One of the advantages of boost pressure regulation is that the engine can also be run safely on gasoline with a lower octane rating, although not lower than AON 87. However, engine performance will fall slightly and heavy loading and laboring should be avoided. For optimum performance, use the recommended grade of fuel. • The maximum boost pressure is regulated according to the tendency of the engine to knock. Short-lived knocking is perfectly normal. This can occur when the engine is running at about 3,000 rpm under a heavy load. The extent of this knocking will depend on the grade of fuel in the tank. • Isolated instances of knocking can occur with low-octane fuel. This controlled form of knocking, followed by a reduction in the boost pressure, is a sign that the control system is working normally, and is perfectly safe for the engine. Important considerations for driving 1 Starting and driving • Do not use full throttle until the engine is warm, so as to avoid unnecessary wear. If the needle of the turbo gauge repeatedly enters the red zone, the engine may suddenly lose power, due to the initiation of a monitoring system that limits the boost pressure. Contact a Saab dealer as soon as possible. • Under certain barometric conditions (high outside temperature and/or high altitude) the needle may enter the first part of the red zone without necessarily indicating that a fault has arisen. • A protective function (interruption of the fuel supply) limits the engine speed. NOTICE • If the engine sounds strange there is a malfunction. Contact a Saab dealer immediately. • The use of fuel with too low an octane rating can cause serious engine damage. Limp-home The engine management system has a diagnostic feature that checks a number of internal functions. If a fault is detected in the throttle valve, the engine management system will set the throttle system to the limp-home mode. This means: • idling control will be poor (uneven idling since regulated by ignition and fuel supply) • engine performance will be reduced • the cruise control will not function • the capacity of the A/C compressor will be limited.