Confused

My car is acting VERY strange.When I shut the car off the guages seem to move up and down alittle bit.And when I start it up(after its warmed up)it takes forever to decelerate when I rev the engine.Anyone have any ideas because i’m stumped.

if it’s the cobalt take it to the dealer

rev prob might be the idle air control

prob the skyline muffler

Exactly, what kind of vehicle is in question?