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!
first, mortgagee lenders will only lend money against property that they can securely place a lien against (and for which they can transfer the loan). they will not want to lend money towards "buying" the car. i see lenders demand that such items be removed from contracts all the time.
second, if you are giving the car away, you may incur gift tax liabilities (then again, i am not a tax preparer and you MUST NOT take anything here as tax advice. The IRS really frowns on this sort of thing)
i'd review this with your legal counsel for a more formal opinion before you proceed.