Will Peugeot 308 refit the air inlet increase fuel consumption?

It will definitely increase. Firstly, the fuel injection quantity should be controlled according to the intake air quantity. If the intake air reaches the mixing ratio, the fuel injection amount should be changed. Secondly, the oxygen sensor also needs to detect the oxygen content in the exhaust gas to meet the emission standard, so it will also control the fuel injection quantity.

From the point of view of theory and practice, it is suggested not to modify it. Instead of repeated investment, it is better to change a car that meets your own requirements.