A friend of mine has a Chevy Corsica,1990',4 cylinder,65,000 miles on it.he said it ran good night before but would not start the next day and still won't.Its getting fuel,cranks good and he said plugs are firing fine.He said the only thing he noticed was the idle pulled down when he switched rear defroster on.Any ideas on what it could be,I gave him several already but he is no mechanic.What could a novice check to find out what it is ?Its also been like -11 below where he lives if that helps.. And notice I'm saying HE...