A particulate coke composition including expandable coke is capable of removing deposits from rotating parts of a gas turbine engine while under full fire or idle speed. The coke composition may be introduced directly into the combustion chamber (combustor) of the gas turbine or, alternatively, anywhere in the fuel stream, water washing system, or the combustion air system. By kinetic impact with the deposits on blades and vanes, the deposits will be dislodged and will thereby restore the gas turbine to rated power output. If introduced into the compressor section, the coke particles impinge on those metal surfaces, cleaning them prior to entering the hot gas section where the process is repeated.