1998 Ford Explorer intermitting starting

My 98 explorer has an intermittent starting problem based I think with the Anti Theft System. Most of the time I can walk away with the key for about ten minutes and it will start. Other times not. I have tried to disconnect the battery thinking this will reset the system and Voila. Today I did the same thing and nothing. I have on two occasions gave the air intake (fuel injected) a shot of ether and both times it started but I don’t want to continue this practice for obvious reasons. Any ideas? New fuel pump 2 months ago. The anti theft light blinks while attempting to start. I have an after market remote start but this doesn’t work either when I am having this problem. When I turn the key on the theft light comes on for about ten seconds then goes out but the car started right after that