The VUV spectrum of foil-excited argon ions has been observed with time delays of up to 20 ns after excitation in a search for the intercombination lines of Mg-, Al- and Si-like ions. In Ar 6+ the intercombination line has been identified and its wavelength has been determined with a precision equal to that achieved in a recent tokamak experiment. In Ar 5+ and Ar 4+ the signal is expected to be lower by one order of magnitude because of the longer lifetimes. We discuss possible identifications of very weak lines with the transitions of interest.