How much do you identify with the type descriptions of ISTP vs. INTP? You may just be someone who is on the border between the two types. My husband is like that. He first tested as ISTP, then INTP in later years. He comes across to others as INTP because he is very intellectual and can go into long explanations of topics he is interested in. However, things that SPs say about their preferences, such as their tendency to run up the stairs at airports (while loaded with baggage, backpack, etc.) instead of taking the escalator, strongly preferring driving stick-shift instead of automatic, fit him well. He also has a real interest and knowledge of tools for his hobbies- he has to have the
right tool for the project at hand.

It's pretty confusing trying to figure his type out!
Edit: He likes riding motorcycles, too.
If your avatar photo is of you, your eyes seem pretty intense and serious. You look like an ISTP to me, FWIW.