Vibration when the car's on IDLE, but the car was hit underneath (front)

What is your question?

I accidentally hit the car underneath by going on a center median in the middle of a parking lot (it was almost like a sidewalk-but diving the center of the parking lot) and the plastic from the front (underneath)came off and the car has had a vibration when on idle. I accelerate slightly and the vibration goes away-but I have to keep the accelerator down to keep it from shaking slightly. It's not a tremendous amount of vitration but it wasn't there before I hit the car underneath????