Dan,he has 1/3 of it correct.The idle will not change on the older cars.The timing does not retard,just stabilises (sp).But,the check engine light should come on when connector is shorted.I have seen several that act like yours,but our smog tests don't require all that BS,so I have never looked into it any farther.Sorry can't be of more help,maybe some else can add more comments?
Shawn
Shawn