Don’t you measure resistance on the iac solenoid pins to see if the coils  are still intact and measure the same. also if you still have AC what happens when you turn it on, Does it still idle faster and slower again when AC off.

Hmmm yeah not sure, when car is on the IAC sensor receives 13.8v on the middle wire which is normal I think. It only faults when I decelerate for a long period (I.e down a hill) then it goes into low power when I accelerate more than half throttle the first time after the deceleration, then the check light turns off and it drives fire until the next deceleration 

Time to pull out the multi meter and measure resistances. But doesn’t the IAC share some wiring with the o2 sensor maybe the old sensor blew a fuse or one of the ignition relays.

came across these "Paid" files   Spotlight Cover's : Headlight intake's etc not cheap BUT I thought some were neat   https://cults3d.com/en/design-collections/GiaoPX/subaru-impreza-gc8

codes cleared took it for a drive and code 24 popped up again after about 10minutes, wouldn’t let me boost fully and went all slowy  Idle Air Control looks like I’ll be pulling it out this weekend