The Zohar, Ra'aya M'hemnah, in Parshas Tzav says that Teiku means it will always stand as a question, as it stands for *Tikun* minus the *nun sha'arei Binah* (the 50 [=Nun] gates of understanding). 

It goes on to say that Eliyahu will answer other ones that do not end in "Teiku".  This contradicts the tradition that YS quotes. As usual, this Zohar needs a Rebbi to explain it.

רעיא מהימנא ספר ויקרא פרשת צו דף כז/ב I can't find an online source yet...

and the [Biur HaGra][1] on it.