i need some ideas.

I have a 2000 bravada and i love it.  I have had no issues from it until today.  
I had to change the thermastot.  The changing of the thermostat went
awesome smooth.  It was all put back together and i put my son to bed.  I
had my mom watch him so i could go to town.  It was running perfect until i
got to the store (2 miles down the road) when i got to the store I put the truck
in park and it started to jump on the idal.  i drove back home instantly and my
dad re connects a hose that was coming off of the breather.  i started the
truck as my dad had instructed.  for a little bit it started jumping rpms from
like 500 - 1500 rpms than evened out. as i drove the truck it was fine. i know
i had some low oil so we got some oil in it.  The check engine light is still on
and when i start the car for about 5 mins the rpms keep bouncing than even
out.  i have no idea what else it could be.  please help me out here with
ideas.