Hey guys.
My MY99 WRX is due for a service but just in the last few days it has been revving very jerky when it comes on boost. Im a bit worried so I wont be driving it until my mechanic gets back from holidays and can look at it.

Any ideas? Could it be misfiring? Bad plugs? Coil pack? Vacuum leak?

Im not hugely tech savvy when it comes to cars so any suggestions would be great