Anytime you do a major modification to your engine, you need to adjust the ECU program on a dyno. Only on a dyno can you see the fuel air mixture as well as the torque output across the RPM range and range of throttle position. Trying to tune a car on a street is not very effective.

Otherwise, please explain your problem by telling the RPM you at not the speed. The engine and turbo don't care how fast your going, only the throttle positon and RPM.


To answer the question directly. Most likely the fuel mizture is too rich or lean at that RPM and throttle position you were describing. Either the turbo has created a set of parameters that are outside the adjustment range of the ECU, or it could in fact be a vacuum related problem as you describe. I'd get a service manual and figure out the correct hose routing and what the function of each connection is.