Dart wont stay running

I have a 72 Dodge Dart Swinger, 225ci, 2bbl, was running great two weeks ago now when I start it all it wants to do is sound like its fighting to stay running and then it just dies. Was thinking it could be air leak. I put it in drive and reverse and it then seemed as it was just fine but as soon as i put it in park it wants to die. Any ideas?