Low rpms with a new battery

[jaimico]

Yesterday my 2008 yaris sedan battery just past the way, and I replaced it with a bigger model (from 350 to 500 cca), since I could not find the same size or capacity as the original.

To my surprice, after replacing the battery, I started the car right away, but the rpms just when to the minimum, like 300-500 at idle (normally are around 700), it was like having a 3 cilinder engine, let it run for a while, but did not change, so i took it for a good run, and still the rpms where dropping at idle, and suddenly it just came back to normal.

Today i had my 50K maintenance, and when I came home disconected the battery to adjust the supports, and when I started the car again , the same problem again, but this time at a smaller rate (the rpms where around 500 know).

So, is it something with the car computer the need to adjust after a while, or what??, since the alternator was chargin normally.