I don't think there's too much common in INTP and ISTJ types.
INTP is more likely to be too interested in the details than ISTJ. Sounds weird? I think ISTJs are actually more interested in the mere outcome that events leading to it. Us ISTJs are often pragmatics, who prefer to apply tools that are known to work.
I haven't watched too much of Big Bang Theory, but to me Sheldon doesn't feel S at all. He's so N. Definitely an N. Also ISTJs prefer dogs over cats.