wierd idle

[2012 Mustang GT]

when i turn my car on the idle is about 900 and if i touch the gas the RPM's go up than down to around 600 RPM is that normal

i sont know if the computer is confused because me and my dad changed to timing and i marked the balancer wrong and it was set at 2* for a few days and i just found out and now it is currently at 10*

any opinions?

 

[2012 Mustang GT]

is that bad or is it normal? for the idle to do that

 

[ironmedic]

that is normal for a car to start up that way that has been sitting a while. its practically an automatic choke.