You'll most likely have a hole or tear in one of the intake hoses/boots causing a vacuum leak. These run from the air box to the intake manifold and brake servo.
Check everything between the airbox and the throttle body, take it all off and clean it up. Remove the idle control valve and give that a clean as well. Inspect the seal on the DISA as well.
If that's not the issue, at least you've given everything a clean up, and it will only take you an hour. This is good preventative maintenance anyway.