Air leak i would almost definitely say.

With an MFI system everything connected into the system is detrimental to the good running of the engine, if anything develops an air leak you will have running problems.

Check hoses intercooler etc for splits/air leaks.

If not try disconnecting the long breather pipe that runs from the rocker cover to the air flap and block the hole in pipe in the air flap box.

Failing that try also disconnecting the brake servo vacuum pipe and once again block the hole into the inlet plenum.