Method for detecting coking in the intake tract of an
internal combustion engine with direct
fuel injection,
throttle valve and variable intake
valve lift control, comprising the following steps: - Determining a correction value (KW) which is calculated by the intake
valve lift control as an offset value with a preset
valve lift; - Performing an initial quantity deviation test, by which an initial air-fuel
ratio value (w1) is determined from a
lambda value (λ) measured during the initial quantity deviation test. real, 1 ) and a desired
lambda value (λ soll, 1 ) the fuel
combustion in the
combustion chambers of the
internal combustion engine, whereby in the first quantity deviation test a load control is carried out by means of the variable intake valve lift control; - Performing a second quantity deviation test, by which a second air-fuel
ratio value (w2) is determined from a
lambda value (λ) measured during the second quantity deviation test. real, 2 ) and a desired lambda value (λ soll, 2 ) the fuel
combustion in the combustion chambers of the
internal combustion engine, whereby in the second quantity deviation test a load control is carried out by means of the
throttle valve; - Determining a comparative result (VE) from the first air
ratio value (w4) and the second air ratio value (w2); - Determine whether coking is present in the intake tract of the internal combustion engine by combining the comparison result (VE) and the correction value (KW).