Originally Posted by Sal329
Dirty MAS? Sometimes the oil from the cleaning agents of the air filters get on the MAS and could cause a problem like that.
You may also want to check what fuel pressure is the fuel pump making,
5psi difference will make a big difference on actual fuel injected since it is a exponential relationship between fuel rail pressure and actual fuel injected trough the injector.
So you may also want to make sure that the pump is indeed in good shape...