I am not sure whats going on but after running around when I come to a stop and put the car in park my engine seems to rev up and down for a couple of seconds and then it levels out. It only does this after I put into park. Does anyone have any info on this? Also the other problem, I noticed is I recently charge my ac unit and now every now and then if Im just idiling at a light my car will shudder for a second and loose rpm's and then smooth out again.

If anyone has any info regarding this please let me know
Thankyou
Jason