A motor fuel additive composition comprises a mixture of: (a) from about 5 to about 50 weight percent, based upon the total weight of the additive, of a detergent component selected from the group consisting of (i) a reaction product of a substituted hydrocarbon and an amino compound, and (ii) a polybutylamine or polyisobutylamine; and (b) a fuel conditioner component comprising (i) from about 2 to about 50 weight percent, based upon the total weight of the additive, of a polar oxygenated hydrocarbon compound and (ii) from about 2 to about 50 weight percent, based upon the total weight of the additive, of an oxygenated compatibilizing agent. The fuel conditioner component may additionally comprise a hydrophilic separant, an aromatic hydrocarbon, or mixtures thereof. Additionally, in some cases the hydrophilic separant may also act as the compatibilizing agent. The additive may also additionally comprise a carrier oil or fluidizer. The additive is prepared by mixing together the detergent and fuel conditioner components, and is advantageous in that the detergent and fuel conditioner components synergistically interact to reduce both fuel intake system deposit formation and combustion chamber deposit formation, thereby inhibiting engine ORI.