Toyota Celica Running Lean

[blueforever]

Hello there, I have a 2004 toyota celica T sport and the enging managment light keeps coming on after aroung 200 miles, i got a dignostic done on the car by my mate and he told me that it is running lean. I have replaced the mass air control sensor, spark plugs and air filter, my next step was to check all of the vacumn and breather hoses to se if there was a leak and i was wondering if anyone has had this problem before and if there is a section of the breathe hoses that i need to check first as this is now doing my head in Grrrrrr