trying to fix my parents 06 problem occurred on the interstate it reved up on me and now when i start it the engine revs up to 4k then drops to 500 back up to 4k again then barely stays at idle it doesn't kill but is extremely rough when i do try to put it in gear it does kill any ideas?

 

Hey, first check if check engine light came on and stored any codes, it will be easy way to narrow your parents car problem. It could be numerous things to cause to serg the idle.