I am with Joe on this one. You need to get to the basics of selling cars. Doing things that generate revenue and social is not a bottom line revenue builder. You certainly don't need to spend time on social networks when you are trying to sell cars. I believe in social marketing but not for a struggling salesmen.
1) evaluate the leads you are getting and why they aren't converting (Price, Things you are saying, etc...)
2) Run your own promotion - tell you customers you are running an internet promotion that ends on Sunday. Maybe its urgency you need to build.
3) When you do get someone on the phone during the day while they are at work ask if you can bring the car to them on their lunch break if they are close.
4) focus on your customer and don't give off the impression you are struggling. People love to buy from successful salesmen.
5) Find your mojo and leave your home life at home. Many of my salesmen struggled with their home life and it always effected their sales. (May not be you but just saying)
6) I know we aren't supposed to talk religion but this isn't religion its real....PRAY!
7) Give! When I started giving my income exploded
8) wake early and get to the store before it opens. You get a lot done that way.
No order....maybe #6 first.