An Italian tuneup usually refers to a process whereby the operator of a motor vehicle runs the engine at full load for extended periods in order to burn carbon buildup from the combustion chambers and exhaust system. It is performed after a traditional tuneup and often accompanied by an addition of fuel system cleaner to the fuel tank. It is particularly useful for vehicles that are only operated at low speeds on short journeys, and for diesel vehicles prior to emissions testing.
The origin of the Italian tuneup comes from Ferrari. Owners would drive their cars infrequently and never run them hard, which causes the engine to build up enough carbon inside to affect performance. Mechanics would perform a "tuneup" by driving several laps around a race track to get the engine hot enough to burn out the built up carbon. Cars before the advent of modern engine lubricants and fuels, often had a 'de-coke' by hand, after removing the cylinder head, as a scheduled service operation.