Sounds like you got a issue , I had a standard v4 uk2000 which was 230ish but kept up with my old 36 m3 but it's the lightness of the scoob that makes it quick
You can blank off the dump valve and I done it but it kills turbos so get a spare or 2, if it's on. Td04 then expect to pay about 25-40 quid for a replacement , they used to be cheaper but the glanza owners like them so pushes the price up
Check the maf as well give it a quick clean first but they are prone to fail quick if your running a cone filter