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... ;-)
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.