acrmnsm

My 2005 Tourer 2.2 developed a fault while driving, lost all power as if the turbo had failed, and the glow plug light kept intermittently flashing. ODB said P1237 lack of boost?Anyway my decent local garge pluggged in their fancy ODB and said it seems like air mass flow sensor, which was a cheap and easy replacement, and a new air filter. The car now drives better, but seems to hit a wall at 3k, however with the air filter out it will rev all the way to the redline. It is not giving any fault codes now. Any ideas? Same problem with old filter too. Tried all pipes, no leaks, splits or fit issues. We have replaced air mass flow sensor, map sensor, cleaned egr, checked intercooler, turbo. its wierd. Take out air filter it runs like a dream. Anything else other than chucking it off a cliff?