Rally mode selects boost enhancement for rally cars on throttle back off. When the throttle position signal is BELOW the pre-set TPS level AND when the engines RPM is above the pre-set RPM level, the boost enhancement feature is enabled. When the boost enhancement is enabled the ECU misfires the Ignition (see Ign. Fire), retards the timing (see Ign Trim) and adds fuel (see fuel trim). This feature would be used in conjunction with an auxiliary o/p to energize a blow off solenoid valve to either bypass the throttle body or to blow air directly into the exhaust manifold near the exhaust ports