After starting a 2008 Suburu Tribeca (automatic), the engine idles at around 1600rpm. Even if I leave it for a few minutes, the revs don't change.
But, if I even slightly tap the accelerator, the revs drop from 1600rpm to around 900rpm (and stays there). This happens in both hot and cold whether, but it doesn't happen when the car is stopped at lights or in traffic; I've only noticed it when starting the car.
I've searched the internet but found no information on this. I also haven't seen this happen in any other car, so I doubt it's expected behaviour. 1600rpm when idling also seems unusually high.
What could be causing this to happen?.