Vauxhall Vectra obd p2279

I am getting either a mil illumination,or a small yellow engine illumination on my dash board.I have done an OBD test,and it throws up the code P2279,air leak on intake system.This problem only come up when the engine is at running temp 85deg,and acceleration is required on higher speed roads.The car starts fine,runs smoothly so no problems in that department,It has recently been MOT'D and fully serviced.Ihave cleaned the EGR valve,and replaced the Boost sensor,I have also been to the garage and had help from them no split pipe found,(Ether test),swirl valves appear to be fully operational,Once light on and at temperature,there is a distinct lack of power,the car struggles on inclines,is sluggish on acceleration and will not pass 3000rpm,As much as I hate to say this,I still like the car,but am at my wits end with it,if a solution cannot be found I will have to get shut of it.