What we have been seeing in the current market is that most buyers will not bite on a promotion such as this. It is great for getting attention, but in the end, the buyers that we are working with will try to negotiate "out" the car, meaning that if you are willing to take $300,000 for the house, and throw in a car worth $8500, then why doesn't the price adjust to $291.500, and then leave the car out?
As others have mentioned, it is also difficult for lenders and appraisers to wrap their heads around such concepts, and it's generally best if any mention of the car is left out of the contracts (please consult with your attorney first).
If you can sell the car before you list the home, you could use the cash from the sale to induce buyers in other ways, such as paying closing costs, assessment fees (if there are any), future property taxes, etc. Make sure to check with your attorney to ensure that anything you offer will be legal and "above-board", and also double check with the prospective buyer's lender to make sure there are no restrictions on the types of credits you are offering.
Hope this helps! Good luck!