Engine problems

As far as the rpms goining crazy you might also want to check the egr valve if equiped with one and the idler control module as well. Those two things can have a huge affect on the idle of the vehicle. The idler control module should be located at the throttle bottle of the intake, but do not mistake the module for another. The best way to go at it if your unfamiliar with how is looks is looking the part up on google, then maby you might find a diagram of where exacly it is located.

Hope this helps!