The [Zohar, Ra'aya M'hemnah, in Parshas Tzav][1] 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). This is used as a signal that this question comes from the *klipos* (shells) and could not have an answer because the halacha it is addressing has an element of *gezeirah* (divine decree) to it and not fully understandable by Man.

It continues on to say that Eliyahu will answer other questions that do not end up as "Teiku".  This contradicts the tradition that YS quotes. As is usually the case with *sod* (the hidden parts of Torah), this Zohar needs a Rebbi to explain it.

[רעיא מהימנא ספר ויקרא פרשת צו דף כז/ב][2] 
and the [Biur HaGra][3] on it.