Engine starting and warm-up fuel control method having low volatility fuel detection and compensation

A method of operation for an internal combustion engine having an open-loop fuel control for maintaining an air/fuel ratio of said engine at a target value during engine starting and warm-up, comprising the steps of:

• measuring a speed of said engine during engine idling following starting;
• determining an engine speed error based on deviations of said measured speed from a desired idle speed;
• bandpass filtering an error signal based on said determined engine speed error to form a surge signal representative of speed error fluctuation in a predetermined frequency range attributable to usage of high driveability index fuel in a cold engine;
• low-pass filtering said surge signal to determine a sustained amplitude of said surge signal;
• detecting usage of high driveability index fuel if the sustained amplitude of the surge signal exceeds a calibrated threshold;
• and
• temporarily enriching said air/fuel ratio relative to said target value when the presence of high driveability index fuel is detected.