Oracle Database Discussions

Hi,
I have a query which was taking long time than usual.
After analyzing the query and run explain plan for that, we have found the particular table go for an bit map conversion.
In my environment the oracle hidden parameter "_b_tree_bitmap_plans"=true.
But if i use no-index hint in my query the query looks normal,but plan shows that cost for the full table scan was quite high
If i use index the query takes long time,.
So how to recover from this issue.
But in my environment the management will not allow me to change the hidden parameter ("_b_tree_bitmap_plans") to false.
Kindly suggest me on this

Regards,
Faiz