Try checking you're iac Idle air control if its bad or going, it's on the throttle body!

 

That's happened to me where the cable sticks after driving for a while and the engine revs at 4k in neutral and standing still. I just loosened the cable a bit. When it's becomes really hot or cold weathewise it tends to happen to me because the cable expands or contract a bit and sticks . Hope you get ir resolved quickly

 

The throttle cable was sagging when it got hot. It's been reattached, so now everything is working just fine!