S40 idle surges up and down while in park. Put it in gear and it stays level but fast. Do i have a vacuum leak? If so where to start looking?

 

Get a can or carb cleaner and start the motor in park. Spray around the intake duct work and intake manifold. If you can change the idle or kill the motor by spraying the carb cleaner at a certain spot, well you have found your intake leak. If not check the function of your IACV.