i have 2 tabs.

sheet1 -- contain list of name and id#.
ID# (sorted), Name
101
102
103
1001
1002

sheet 2 -- contain id#
ID#. Col. B
101
1001
102
103
1002

in sheet 2, i want to check if the id# exists in Sheet 1, and if does, i
want it to display the id in col. b.
=VLOOKUP(A1,Sheet1!$1:$100,1)

When, i do this, most of the time, it works, however some time the result
does not come exact.
Like if it was looking for 1002, the result will show as 102 and end.

Formatted all col. as text. what can i do to fix this.