From Longman Dictionary of Contemporary Englishbe fixing to do somethingbe fixing to do somethingAmerican English spokenPREPARE to be preparing to do something – used in some parts of the US I’m fixing to go to the store. Do you need anything? → fix
Examples from the Corpus
be fixing to do something• I'm fixing to go to the store. Do you need anything?• He was fixing to get rid of the first one in the divorce courts. 