Method of operating an internal combustion engine

A method for operating an internal combustion engine in the form of an Otto engine, especially of a motor vehicle, selectively uses carburetor fuel, especially gasoline or ethanol (E85) by direct injection into at least one combustion chamber of the internal combustion engine by means of at least one fuel injector. Optionally, instead of injecting ignition spark engine fuel or in addition to injecting ignition spark engine fuel, the internal combustion engine is operated with gas, especially CNG (Compressed Natural Gas) or LPG (Liquefied Petroleum Gas). A mixture adaptation value is continuously determined during the operation of the internal combustion engine with spark ignition engine fuel. An actual mixture adaptation value is stored in a memory during the operation of the internal combustion engine with the spark ignition engine fuel and, after a predetermined minimum duration of operation with gas, an actual mixture adaptation value is compared with the stored mixture adaptation value during the operation of the internal combustion engine with ignition spark engine fuel. The fuel injectors are scavenged when a difference between the actual mixture adaptation value and the stored mixture adaptation value exceeds a predetermined difference value.