Drinking too much
beer in Munich ;)
Join Date: Feb 2012
Location: I would rather not say
A good place to start would be to reseat the connectors for the sensors, MAP, MAF, Boost control solenoid which will give you a visual confirmation that they're connected properly and you don't have a loose plug.
The MAP sensor could be very dirty, especially if the car is standard and has a few miles on it. It's located in the air intake and comes out easily by removing one torx screw, The 'basket' section in the inlet manifold houses the temperature sensor and the MAP sensor itse'f is in the housing part which sits outside of the manifold. There needs to be a clear path down through the basket into the sensor housing, it gets very gunged up.
Another good place to start though, is to get a cheap ELM327 diagnostic cable or bluteooth interface, and if you have a laptop use some of the free fault code readers to find out what the ECU thinks is the problem.