the use of 'just' in present perfect

The meaning in sentence 2 is just as clear as in sentence 1, and it means the exact same thing, but it sounds awkward and incorrect to me. I think that in that context, using "I just have" is wrong, but I'm not entirely sure.

If you were saying it and only implying the verb, as if someone had just asked you "Have you had lunch?" and you were responding without explicitly restating the verb, than it would be fine to say "I just have" although it would probably be more usual to say "I just did". But you would never say "I have just" unless you were going to finish it with an explicitly stated verb.

Hope that helps.

Echo