A fuel control system that estimates the fuel quantity received from purging of an evaporative emission control system and then accounts for the purge fuel in determining the amount of fuel to be injected into a cylinder of an internal combustion engine. Purge fuel quantity is represented by a purge equivalence ratio which is computed based upon an estimate of the hydrocarbon concentration in the purge gas. The hydrocarbon concentration is adaptively learned using an iterative routine that updates the estimate based on the integrated error between the actual and desired air/fuel ratios. Wall wetting and closed loop corrections are applied only to the non-purge fuel portion of the total fuel delivered to the engine cylinder. The closed loop control includes a block learn memory that provides a correction to the factory fuel calibration. The hydrocarbon concentration is updated using the integrated error during purging, whereas the block learn memory is updated using the integrated error during periods when no purging is occurs. The evaporative emission control system includes a solenoid-operated purge valve that is controlled in a manner that provides improved fuel control during transient conditions. The solenoid duty cycle is controlled using a purge factor that operates to reduce the duty cycle when the intake airflow rate drops significantly.