Terraclean cleans carbon from the valves, piston crowns and combustion chambers. It doesn't clean sludge out of EGRs, and VAG EGRs are generally too fragile to take off and clean anyway. EGR problems are typical of the EA189 1.6 TDI anyway and are almost inevitable after the NOx emissions fix. I think this is more than coincidental and that VAG should replace the EGRs FoC. Volkswagen dealers have been charging up to £1,200 to replace EGRs.