The invention concerns a detergent and anti-corrosive additive for engine fuels, in particular gas oil, containing amide or imide functions characterised in that it is obtained by mixing wt. 60 to 90% of a compound A consisting of at least one carboxylic polyalkenyl, diacid or anhydride, of average molecular mass between 200 and 3000, wt. 0.1 to 10% of a compound B consisting of at least one carboxylic compound, monoacid or anhydride, containing 1 to 6 carbon atoms per chain and 10 to 30% of a compound C consisting of at least one primary polyamine of general formula H.sub.2 N--[--(CHR.sub.1 --(CH.sub.2).sub.p --CHR.sub.2).sub.n --NH].sub.m --H, the mol ratios A/B/C corresponding to 1/(0.1 to 1)/(1 to 3), A/B/C never being 1/1/1.