I see a lot of questions whose full meaning cannot be derived without noting the tags. (eg 1221534). Another large family of questions which falls into this category is "What's the syntax for ...", which is ambiguous unless there is a language specific tag. Similarly for nearly all questions about regular expressions. Is it appropriate to down-vote such a question, and leave a comment that the question is ambiguous?
No, do not downvote them, as it has been stated before that tags should not be replicated in the title line. We are programmers, we hate redundance. And obviously, the ambiquity can easily be resolved in these cases, just looking at the tags.
There has been quite some discussion on how to write titles:
And then, you might teach people over time to write better titles, but tons of newbies are just scared away if they get downvoted for not duplicating the tag values in the title.
If you have enough rep, and a title really is bad, edit it rather then punishing the question owner.