Abstract: Intake valve deposits in port fuel injected engines are reduced by using a fuel containing a mixture of (a) an oil soluble polyamine selected from (i) an aliphatic alkylene polyamine containing at least one olefinic polymer chain attached to a nitrogen and/or carbon atom of the alkylene radical(s) connecting the amino nitrogen atoms and said polyamine having a number average molecular weight in the range of from about 600 to about 10,000, (ii) a Mannich polyamine comprising the condensation product of a high molecular weight sulfur-free alkyl-substituted hydroxyaromatic compound wherein the alkyl group has a number average molecular weight from about 600 to about 10,000, an amine which contains an amino group having at least one active hydrogen atom, and an aldehyde, wherein the respective molar ratio of reactants is 1:0.1-10:0.