The car redlines by itself in neutral? That seems crazy. And certainly isn't good for it
My idle revs increase sometimes. But I'm talking like from normal idle (~1K RPMs) to maybe 2500 or 3000 RPMs at most. It's usually due to dirty MAF sensors or throttle bodies. I clean them and the idle revs settle right back down to normal.
It sounds like you have a different issue though. Hope someone else can chime in and help.