Check all the silicon vacuum hoses associated with your turbo, I found one of mine had been damaged from heat and replacing it stoped the problem. Be mindfull that if u remove the hose with the "boost pill" that you may continue to have boost problems unless u get a verso tune or similar (I had this done on my bug). From memory u can tell where the boost pill is by identifying a small white mark, almost like whiteout, on one of the vacuum hoses.