What is intellect-consciousness and why is it different from intellect itself? In SN 35.93 quoted below, it reads intellect-consciousness arises in dependence on the intellect and ideas, but if this consciousness is also a thinking about the work of intellect on ideas then it in itself is an intellect. and if so we have to look for another consciousness which higher and the search continues ad-infinitum.

This, of course, is not my own though it's a classic platonic thinkers response to Descartes's misguided saying Cogito ergo sum ( I think, therefore I am),  quoted below is from Plotinos Ennead Book Nine explaining the relation of intellect and consciousness.



SN 35.93 Dvaya Sutta: A Pair


  "In dependence on the intellect &amp; ideas, there arises
  intellect-consciousness. The intellect is inconstant, changeable, of a
  nature to become otherwise. Ideas are inconstant, changeable, of a
  nature to become otherwise. Thus this pair is both wavering &amp;
  fluctuating — inconstant, changeable, of a nature to become otherwise.




PLOTINOS: - SECOND ENNEAD, BOOK NINE.


  Though there be a difference between thinking, and thinking that one
  thinks, these two nevertheless constitute a single intuitive
  consciousness of its actualizations. It would be ridiculous to deny
  such a consciousness to veritable Intelligence. It is, therefore, the
  same Intelligence that thinks, and that thinks that it thinks.
  Otherwise, there would be two principles, of which the one would have
  thought, and the other consciousness of thought. The second would
  doubtless differ from the first, but would not be the real thinking
  principle. A mere logical distinction between thought and
  consciousness of thought would not establish the (actual) differences
  between two . Further, we shall have to
  consider whether it be possible to conceive of an Intelligence which
  would exclusively think, without any accompanying consciousness of its
  thought. If we ourselves who are entirely devoted to practical
  activity and discursive reason were in such a condition, we would,
  even if otherwise considered sensible, be insane. But as true
  Intelligence thinks itself in its thoughts, and as the
  intelligible, far from being outside of Intelligence, is Intelligence
  itself, Intelligence, by thinking, possesses itself, and necessarily
  sees itself. When Intelligence sees itself, it does not see itself
  as unintelligent, but as intelligent. Therefore in the first
  actualization of thought, Intelligence has the thought and
  consciousness of thought, two things that form but a single one; not
  even logically is this a duality. If Intelligence always thinks what
  it is, is there any reason to separate, even by a simple logical
  distinction, thought from the consciousness of thought? The absurdity
  of the doctrine we are controverting will be still more evident if we
  suppose that a third intelligence is conscious that the second
  intelligence is conscious of the thought of the first; we might thus
  go on to infinity
This is just bad translation. "Consciousness" is the common word for vijnana. A better translation of vijnana is "(subjective) experience". Meaning, you see something => you recognize it => you make sense of it => you experience it.

"Intellect" is how they usually translate manas or mind.

So "Intellect-consciousness" or mano-vijnana, is therefore the subjective experience of what's going on one's own mind. It's when you "see" what you're thinking about etc. I think it's called re-representation in modern cognitive science.

It does not require a higher mind or anything like that. Based on my meditation experience, it works as a cycle. Normally the input from sense organs goes to memory to find matching associations, this is how recognition happens, the basis of vijnana. With manovijnana, instead of the sensory organs, our attention grabs data from short term memory, finds matches in long term memory, puts that back in short term memory - voila, manovijnana.