Hi Madcap!

I *love* MBTI stuff and have really gotten into it recently although, like you, I can't seem to get a good fix on my type. I might, maybe, be an INFP - but I'm in no way convinced at this point (but am likely an INxx).

So, first... I think it can be really hard to type yourself. Your primary, first function can be almost invisible to you - because it's so innate and natural and you use it so easily, you don't even realize you're doing it. (That's one thing I've read, anyway). The functions that are harder for you to use tend to get your attention more, you're a bit more conscious of them.

I think any kind of mental issues (you mentioned OCD and autism) can also make it hard to get an accurate read on your type, just an FYI.

For INTJ versus INFP... I've actually looked a lot at these (because I tend to come out somewhere in that arena too). Some thoughts:

1. INTJ leads with Ni, introverted intuition. INFP doesn't use this - they use Ne, extroverted intuition, as their 2nd function.

To me, these have a very different feel. If what I've read/seen is correct... Ni tends to take lots of information and sort of pull it together, like through a funnel almost, to come up with a result, or answer, or conclusion. Once an Ni-user has their answer, they seem quite sure/confident about it.

Ne - tends to be the opposite, they can take an idea, and go in a thousand different directions with it. Rather than move towards an answer, they diverge, and think of all the possibilities. This can create a sense of not being confident in things, because they can imagine so many alternatives.

2. Thinking versus feeling. You've probably seen this all over the place, but don't let the words fool you. You can be a smart, logical "feeler" and can be a kind, thoughtful "thinker".

Feelers make decisions using subjective criteria. With Fi, that criteria is internal to themselves... so it's based on their own values. "Is this thing good for me? Does it align with my values? Do I feel good about this decision? Is this the type of person I want to be?"

Te - which is the 2nd function for INTJ - is all about effectiveness in the world. It's totally different... it's about measuring things in the world, seeing the results of what you do, and whether or not that works.

The problem is... first, since Fi is about subjective values, you can have a value around logic!

Second, according to the folks at Personality Hacker, we often skip our 2nd function in our stack (so an INTJ who is either on the younger side, or hasn't yet really done a lot of personal development work) - could easily skip over Te and over-rely on Fi, their 3rd function.

So... if you're sure it's one of those 2 types, it might be better to look at whether you use Ni or Ne.

Alternatively... you could look at the sensing function. So INFP have Si as their 3rd function - Si is about memory, traditions, and sometimes getting stuck and being unwilling to change. It's worth maybe reading about that function to see if it fits with you, because as the 3rd function in INFP, an INFP might be over-using that (i.e. skipping the 2nd) to go there, and an INTJ won't have it at all in their stack.

INTJs use Se, but in the 4th place. Se is more about actually experiencing physical reality, physical activities (i.e. sports), etc.

Maybe check out the "grip" experience for both types (when they get stuck in their 4th function under stress) or how each behaves under stress, and maybe that will give you another clue?

All that said, I think there's a on of interesting things we can learn from MBTI about ways to think about thinking and parse out behavior/motivations. It's fascinating. Personality Hacker is a great resource, if you haven't checked them out already.

Good luck!