When I start my 2006 Five Hundred the rpms stay kind of high, about 1300rpms, and then slowly drop to normal idle, like 700/800 rpm. Other times the needle will jump to over 2000 rpms on starting and then drop to less then 1000rpms.

What's causing this spontaneous leap in rpms?

Thanks!

 

A lot of engine RPM when cold or first started is determined by what the computer receives as present engine temp.
Higher RPM when cold speeds up warm-up.
Before replacing anything, best to verify engine coolant temp info with a scan tool