My car lost all power when driving, and went into limp more, it came up with 'engine malfunction' warning on the dash. It's been plugged in and came up with turbo low boost pressure and mass air flow sensor issue. I've changed the mass air flow sensor and checked hoses to and from the turbo for any leaks, the turbo actuator seems to be working fine, and it's still the same. Just started it again and now there's an extremely loud knocking coming from the engine when ticking over. Does anybody have a clue what this problem could be?? I need my car back :(

Do you live on the side of a hill? 

Think you need to get it plugged into a diagnostic machine to find out what error codes are shown & take it from there. I believe Forscan is available on eBay & Amazon if you want to find the codes yourself.

P0299 turbo low pressure 
P1103 air flow

are the two codes that come up

The MAP (Inlet pressure sensor) is probably the next suspect. This measures turbo boost, and if reading low, will flag up the P0299 error.

The MAP is also used to cross check the MAF sensor, so it is very possible that a faulty MAP could cause the P1103 error also. (MAP & RPM and Inlet temperature can be used to calculate the air flow into the engine.)

Check the connection to the manifold, the electrical connections, then either test or replace the sensor.

Peter.