Method for manufacturing alkenyl succinimides or polyalkenyl succinimides

is described a process for preparing an alkenyl or polyalkenylsuccinimide comprising successively; a step (a) wherein one prepares an alkenyl anhydride or polyalkenylsuccinic by reacting ene-synthesis of at least one olefin or polyolefin and at least one unsaturated dicarboxylic acid anhydride selected from maleic anhydride and maleic anhydrides substituted by 1 or 2 methyl groups, said reaction being carried out within at least one aromatic solvent selected from toluene and xylenes; a step (b) of reacting the product of step (a) with at least one alcohol or an amine; and a step (c) of reacting the product obtained in step (b) with an amine. These succinimides are used as detergent additives for engine fuels and dispersants as ashless additives for engine lubricants.