M1123 engine revvs up when placed in park

[A1A Detroit Ave]

Hi. New owner of a 2002 M1123. One issue I have is that after driving for a while and putting it in park, the engine rpm's immediately/rapidly go from 1500 to 2500. After 20 seconds or so it goes back to normal rpm's. Is this normal? Something I should check?
Thanks
( learning how to be my own mechanic. Haven't toyed with engines in 30 years. Having fun getting back into it)