Why no así!?
¿Qué era lo que él quería?
Why not Cuál instead of Qué?
Why not fue instead of era?
Why not quiso instead of quería?
4 Answers
¿Qué era lo que él quería?
Why not Cuál instead of Qué?
Cuál is for choosing between several options. We're looking for a general response, hence qué. In this case it's just like English, what did he want vs which (one) did he want.
Why not fue instead of era?
Why not quiso instead of quería?
In all honesty, I can't explain the grammar behind these, but they are correct.
Merely by the way, the sentence in English "What was it he was up to?" is ambiguous, and can mean:
(1) what was he after?
(2) what was he capable of?
In both cases, however, the action or state referred is not aorist.
"What was it he was up to?" = continuous action, even in English, and if only semantically.
hmmm
What was it that he wanted? compared to Which was it that he wanted?
fue and era get a bit more involved... and you should do the exercises about that.