Laguna II 1.9 dci no power

Hi all,

I am a newbie and I would really need your help. i recently bought a 2001 laguna 1.9 dci grantour.
the car was fine when i bought it. after a few days the turbo started whistling adn i decided to change it to prevent major engine damage.
after the replacement the car is just useless.
it starts normally and it has no power. if you push it the yellow engine management light goes on in it drives "normally" in this safe mode.
the mechanic checked the turbo which he says it is ok.
the tester says it is a problem with the intake air.
been already to three mechanincs nobody finds the problem. please help me..