The use of a reaction product comprising a quaternized nitrogen compound, said reaction product being obtainable by reaction a) of a polyether-substituted amine comprising at least one tertiary quaternizable amino group with b) a quaternizing agent which converts the at least one tertiary amino group to a quaternary ammonium group as a gasoline fuel additive for reducing or preventing deposits in the intake system of a gasoline engine or as a diesel fuel additive for reducing fuel consumption of direct injection diesel engines and/or for minimizing power loss in direct injection diesel engines or as an additive for reducing and/or preventing deposits in the injection systems, and/or for reducing and/or preventing internal diesel injector deposits (IDID), and/or for reducing and/or preventing deposits in the injection nozzles in direct diesel engines, said quaternized nitrogen compound being selected from compounds of the general formula Ia or Ib in which R 1 and R 2 are the same or different and are each C 1 -C 6 -alkyl, hydroxy-C 1 -C 6 -alkyl, hydroxy-C 1 -C 6 -alkenyl, or amino-C 1 -C 6 -alkyl, or R 1 and R 2 together form a C 2 -C 6 -alkylene, C 2 -C 6 -oxyalkylene or C 2 -C 6 -aminoalkylene radical; R 3 and R 4 are the same or different and are each H, C 1 -C 6 -alkyl or phenyl; R 5 is a radical introduced by quaternization, selected from C 1 -C 6 -alkyl, hydroxy-C 1 -C 6 -alkyl or-CH 2 CH aryl; R 6 is C 1 -C 20 -alkyl or aryl or alkylaryl; A is a straight-chain or branched C 2 -C 6 -alkylene radical optionally interrupted by one or more heteroatoms such as N, O and S; n is an integer from 1 to 30 and X - is an anion resulting from the quaternization reaction; where the quaternizing agent is selected from (i) an epoxide of the general formula II where the R a radicals present therein are the same or different and are H or a hydrocarbyl radical, (ii) a salicylate selected from such as methyl salicylate, ethyl salicylate, n- and i-propyl salicylate, and n-, i- or tert-butyl salicylate; (iii) an oxalate selected from dimethyl oxalate and diethyl oxalate; and (iv) dimethyl carbonate. a) of a polyether-substituted amine comprising at least one tertiary quaternizable amino group with b) a quaternizing agent which converts the at least one tertiary amino group to a quaternary ammonium group R 1 and R 2 are the same or different and are each C 1 -C 6 -alkyl, hydroxy-C 1 -C 6 -alkyl, hydroxy-C 1 -C 6 -alkenyl, or amino-C 1 -C 6 -alkyl, or R 1 and R 2 together form a C 2 -C 6 -alkylene, C 2 -C 6 -oxyalkylene or C 2 -C 6 -aminoalkylene radical; R 3 and R 4 are the same or different and are each H, C 1 -C 6 -alkyl or phenyl; R 5 is a radical introduced by quaternization, selected from C 1 -C 6 -alkyl, hydroxy-C 1 -C 6 -alkyl or-CH 2 CH aryl; R 6 is C 1 -C 20 -alkyl or aryl or alkylaryl; A is a straight-chain or branched C 2 -C 6 -alkylene radical optionally interrupted by one or more heteroatoms such as N, O and S; n is an integer from 1 to 30 and X - is an anion resulting from the quaternization reaction; (i) an epoxide of the general formula II where the R a radicals present therein are the same or different and are H or a hydrocarbyl radical, (ii) a salicylate selected from such as methyl salicylate, ethyl salicylate, n- and i-propyl salicylate, and n-, i- or tert-butyl salicylate; (iii) an oxalate selected from dimethyl oxalate and diethyl oxalate; and (iv) dimethyl carbonate.