Grinding noise and idling issue after hitting a deer

Oh deer. Sorry I just had to say that. First things first, go get a scan done and see what the code is, lets get that sorted first.

Hitting a deer can do a lot of hidden damage. The front of the car could look fine but under all the plastic things get damaged. I would look under the hood to see if the engine shifted in the cradle or if the header panel (the part the radiator is on) moved enough that it hits the engine. If you do not go under the hood very often it might be better to take it to a shop and have them look it over and see what they find. Or if you have an automotive friend have them look. I have seen more than a few cars hit a deer, some looked like it never happened, but the parts under the panels were destroyed. Hopefully your issue is something minor.

What was the exact code set?

Lean code is probably a knocked loose vacuum line or broken plastic parts as there are a bunch of them on and around the engine. Some seem to break if you just look at them wrong. However, looking at the damage, you may want to pull the front bumper cover and look close as I would bet the impact absorber and support are damaged and likely the header support is bent as well. The grinding noise, did you need to be moving or was it there while setting still with the engine running?

DUCT-Air Cleaner and Silencer. Best place to get one would be a salvage yard or you-pull-it type place. From a dealer it is around $100.00 to $175.00 depending on the dealer.

Grinding only while stopping- check the brakes over for damage as well as for any low hanging plastic under the car.