1990 300zx

[timtim230]

last night i got into a wreck and hit a pole backwards. it didnt seem to mess up much but the rear bumper smashed in and bent the back up pretty good. When i start the car the idling is weird though it keeps going up and down on rpms. bounces on 1 grand then will rev a little higher and drop down under 1 grand. when im driving it, it has hesitation. What do u think caused this from hitting the back end? thanks!