I was given a sum of money to help subsidize the purchase of a car. Am I obligated to give maaser on that sum?
As an aside, what are the criterion for maaser? Thank you very much.
No, money which is given for a specific use should be used fully for what it was intended for by the giver.
Tzedaka UMishpat Chapter 5 footnote 26, based on SHulchan Aruch C:M 241:5, see Sm”a there 15. See Tshuvos Vhanhagos 2:282. See here for further discussion and general guidelines of Maaser Ksafim.