2001 Alero idle problems

First time user...crazy problem...after car is warm and is turned off..subsequent starts will have the idle bouncing between 750rpm all the way up to 3000! Put it in gear and keep your foot on the brake as it pulsates! Put it in neutral and idle pulsation continues. Traction control light comes on and sometimes Service Engine Soon. Only code I got was a high idle. 0507 or 0705..After car cools down it is fine. Can be driven 3 hrs with no problems but turn it off and the sequence described happens. Ideas?