2006 Audi A4 Limp mode

I've got a Audi a4 2.0 tdi b7 06, it's in limp mode, whenever I take the MAF cable out it works fine so changed the MAF still goes in to limp mode, the EML reads EGR so the mechanic cleaned it and the EML still reads p0404, the car sometimes drives normally for about 30 seconds and then goes back into limp mode, what could the cause be?? Thanks