I'm a (idea)

Modern hip-hop slang for "I'm going to" (or, more probably, "I'm gonna").

Cf. the following song lyrics:

• "I'm a name her Bonnie" (Eminem - Stan)
• "Baby, I'm a do right" (3LW - No More)
• "I'm a do things my way..." (Limp Bizkit - My Way)