No, the money is what I give you instantly, if Im lacking something of actual value you want to barter for the car. In my example you wanted a diamond ring for the car, that is what you will get at a later date, by trading my IOU (money) either with me or someone else for a diamond.
So the money for us must represent a diamond. However, a certain amount of money does not represent a diamond: it represents the
exchange value not only of this diamond, but of anything having the same exchange value. If money meant "I owe you a diamond," then it could not buy anything other than a diamond, which means it could not
buy anything---since by definition money does not care what it buys, provided it has the same exchange value it has.
Nobody actually wants money, we want what we can buy with the money, ie, collect the debt it represents. If the money doesnt represent a debt, its quite worthless.
We want money because we want to be able to buy things, mostly not yet knowing which ones. Money does not represent what we want to buy: it rather represents its exchange value.
No amount of money makes any decision about what we can buy with it: that is precisely the point of money: the capacity to represent exchange value, giving us absolute freedom about its concrete form.
If I have U$ 100,00 and a pair of shoes worth U$ 200,00 and you have U$ 200,00 and a knife worth U$ 100,00, I can give you my pair of shoes while you give me U$ 100,00 and your knife. In the end, we still own U$ 300,00 each, both in monetary and commodity form, and nobody owes anybody anything.
We just agree on a value denominated in something abstract, that used to be gold and now we call it dollar or euro...
Here you are close to defining money, except for the word "abstract": money is a
generic exchange value denominated in something
concrete.
In the above example, the debt is what i owe you for the car. The money you get serves as proof of what you are owed by the issuer of the IOU, be it me or a bank. The money itself has no value, other than the debt it represents.
A monetary debt consists in owing not an object, but rather its exchange value. If I owe you U$ 100,00, I can pay you with anything worth U$ 100,00 (although I suspect you will prefer money so you don't have to sell whatever I give you to get what you want). So any monetary debt requires an independent representation of exchange value. If a monetary debt were itself the owed exchange value, then it would become an infinite regression of the form: someone owes the circumstance of someone owing the circumstance of someone owing the circumstance... to someone else.