With such a low daily budget is it possible your ad will NOT show (even when a search on your keyword is done) at times because Google is spreading the budget out over the day?
About Daily Budget
[webmasterworld.com...]
Take that post into account with this quote:
BTW, I've noticed that if you have a lot of keywords that have CTR of 4% and above, then the system that calculates the recommended budget can be 'fooled' into saying your budget is OK, when in fact your ads may not be showing all the time. This is because the system calculates using a low-average CTR of around 2%.