An internal combustion engine for a vehicle has an exhaust gas recirculation system for returning exhaust gases to the engine intake passage. The carburetion system for the engine includes a fuel enrichment valve. A control suction air line from the intake passage operates a regulating valve which controls the exhaust gas recirculation valve as well as the fuel enrichment valve. The flow resistance through the control suction air line is controlled by a prescribed control factor, which factor may depend upon the engine temperature alone or supplemented by engine speed, engine load (suction pressure), or atmospheric pressure.