I think this is what you want:
(\d)\1(\d)\2
Find a digit followed by the same digit, followed by another digit (possibly the same) followed by the second digit.
Edit:
If the pairs of digits must NOT be the same, (i.e., 2222 should fail), then you can add a negative look-ahead like:
(\d)\1(?!\1)(\d)\2
You can use the
Expresso[
^] tool (free) to build/explore/learn regular expressions.