I think DL should accept/adopt the translation: "Πρόκειται να αγοράσω αυτοκίνητο." The numeral "ένα" gives emphasis to the purchase of one car (and no more than one cars), which is missing from the English sentence.

Using the wrong i letters in αυτοκίνητο sometimes is a typo and sometimes a wrong word. Don't be so hard on us, Duo, there seems to be no rhyme or reason to this... ;-)