wierd idling

[obee]

I fired up my car earlier and it was idling around 900 and my brother came out and told me the phone was for me so i went inside and talked for about 5 minutes and when i came back out my care was idling at 2-3oo so i revved it up a couple times trying to see if it would go up a little bit more but it didnt and you barely notice its idling when it does this. so my question is whats up with my idling Any help appreciated