EGR

Exhaust gas recirculation valves were introduced in the car market as a way to reduce gas emissions. Manufacturers created a way to recirculate already burned exhaust gases over to intake manifold in order to be re-burned and this way lowering their emissions. This is basically the function of a EGR valve.

The main problem of this concept is that this exhaust gases bring a lot of engine oils and fumes, that after some time tend to block the intake manifold lowering its efficiency dramatically.