On the forums there was alot of talk about the EGR valve on diesel motors. This valve uses hot exhaust gases and passes it into the intake with cold air. This mixture over time causes the EGR valve to get blocked therefore reducing the cold air uptake:









I had already cleaned my one.. but to save keep cleaning it on a regular basis I bought a Bypass Valve and had it fitted:

Now I have nothing but clean cold air going into the engine. Lovely.