The present invention is directed to a fuel additive comprising at least one adduct of (A) a polyolefin of 300 to 10,000 number average molecular weight substituted with at least 0.3 (e.g., from about 1 to 4) mono- or dicarboxylic acid producing moieties (preferably acid or anhydride moieties) per polyolefin molecule, (B) an amido-amine or thioamido-amine characterized by being a reaction product of at least a polyamine and an alpha, beta-unsaturated compound of the formula: ##STR1## wherein X is sulfur or oxygen, Y is --OR.sup.4, --SR.sup.4, or --NR.sup.4 (R.sup.5) , and R.sup.1, R.sup.2, R.sup.3, R.sup.4 and R.sup.5 are the same or different and are hydrogen or substituted or unsubstituted hydrocarbyl.