You need that encoding incase you are trying to search for the folder name or file name. Remove the encoding and try with free text search query like TEXT:"your phrase". This should server your purpose.
ISO9075 encoding is only required for PATH and QNAME.
Text content is tokenised - which means punctuation () etc will be ingnored. Punctuation should also be ignored when the query is generated. If you encode the () then they wil not be treated correctly.
Always include the actual query you execute - after any encoding you may do ….
So drop the encoding, and put it in quotes.
If you do not put () in quotes (or escape it) it will be treated as part of the query syntax.