Why does your 2002 Renault laguna keep engaging limp home mode?

it's either down 2 ur egr valve it's clogged up with carbon,the turbo pressure sensor or even the wires on the plug that lead 2 the turbo pressure sensor,iv'e now been told it cud b turbo vacuum sensor...these r problems that iv'e gone thru.. i'm just in the process of changin the vacuum sensor,as ive replaced the 1st 2 as nothing changed..car still in limp mode,