1998 Ford Explorer Possible vacuum leak

Engine Performance problem
1998 Ford Explorer 4 cyl Automatic 115000 miles

in the winter my car will start up but the engine dies, all the electrical things still work. It is not the battery because it has been changed and it is still doing the same thing. There is a clicking noise while and after the engine runs. When sitting stil the rpms stay between 0 and 1. In the winter when it first starts the rpms jump to above 2 and will either move up and down between.5 and 2.5 or just go to 0 and shut off the engine. I was told it was some kind of vacuum leak.