Hi Tirebiter welcome to the Forum - can't answer the scantool question as I was going to say the Scangauge II but its a simpler style. Aveos have a heavy drive belt pulley that causes a huge delay in spooling the motor up and down. This can be felt in the pedal when revving the motor. Installing an under-drive pulley solves this issue and adds a few hp.

Also when you mention how it holds revs and the weird idling makes me think of a dirty throttle body butterfly valve actuation or switch which is an easy fix, but if its the electronics of the sensor which seems to be a known issue with some Aveos, some need a new throttle body, or some you can get just the switch.

I have an '08 that had 54000 miles on it that was in almost impeccable condition for its age.. got it two years ago, I think the previous owners were a retired couple that used it as a Church runner (the rear seats were clearly never used).

Car rocks. I just should have rustproofed it as soon as I got it. Car needs that and undercoating every winter to keep the steel. I can't decide whether to totally restore it and keep it for ten years or just run it on the cheap until the water pump goes again. Its such a decent car. Only the manual of course