A sonic nozzle is formed in a recirculation passage interconnecting the exhaust line to the induction passage of an internal combustion engine and a valve member is arranged to vary the throat area of the nozzle, while the induction passage has a similar combination of sonic nozzle and a valve member. The control apparatus has a valve actuating mechanism arranged to link the respective valve members in the sonic nozzles with a common element which is necessarily moved when a change in the engine speed is intended, so that the throat area in the recirculation passage is varied always in direct relation to the throat area in the induction passage.