Okay so today went well, me and my brother finally put a new stereo head unit into my car.. something ive been waiting for forever. Then I drove around, had a good day.. Untill about 15 minutes ago when I pulled my car into the garage, let it idle a bit.. got out to run into the house (to grab something) then I came back out and it had jumped up to about 1100 RPM.. And during that time the check engine light came on. WTF? As soon as it went back down in RPM the check engine light went off..

Im not sure WHY its doing that, the engine has always run really strong, and has been taken care of very well (in our possesion atleast).

Not sure if this could be the cause, but could this be because of my Catalytic Converter? Its been making vibrating sounds lately, and is starting to smell actually. Time for a new one? Could this be the cause?