it's supposed to be for carbon deposits etc. $4 to $6 a can, fairly cheap. It's some oil, naptha, and alcohol.
i guess this is similar to the "put kerosene in your engine oil" treatment for cleaning carbon deposits, but less risky.. i wanna try it out if it'll smoothen the idle (i had an engine flush at the last oil change and it did nothing for my ticking HLA's).