I had a very similar issue. I finally solved it by cleaning the sensor that os between the throttle body and the intake. This helped alot. The next ossue I found was the vacuum line from the DV to the solonoid valves under the intake cover plate plastic. These had failed and I simply moved the DV vacuum hose to a tee at the manifold . Now the boost is linear and aggressive in response to throttle input. 2000TT 1.8 HOPE THIS HELPS althought its 6 years late.