determining whether normal adaptive memory cells or purge free adaptive memory cells are to be used in the adaptive memory cell updates of fig3 both types of adaptive memory cells are contained within the memory 31 of the ecu 27 purge free adaptive memory cells are those memory 31 locations which are updated in fig3 when the purge system 10 is off these cells therefore do not take into consideration the effects of the purged vapor on the richness of the fuel mixture normal adaptive memory cells are those memory 31 locations which are updated in fig3 when purge system 10 is on the normal adaptive memory cells are the memory 31 locations which are subject to possible purge corruption the method begins at block 70 and falls through to decision block 72 at decision block 72 the control system determines if conditions dictate that the purge system 10 should be turned off or kept off while this is a complex decision involving many algorithms some of the parameters involved include the length of time the purge system 10 has been off number of times the adaptive memory cells have been updated rpm map throttle angle and whether the fuel control system is operating closed loop if conditions are right to shut the purge system 10 off the method branches to block 74 at block 74 the purge system 10 is shut off if the system is on or kept off if the system.