96 mc 3.4

I just did plugs and wires on my monte z34, now it won't run in neutral or park. If you can get it into drive without dying, it drives ok and does not die when it is in gear at idle. As soon as you shift to p or n she dies. If it's a vacuum leak, would it run under load, stopped in gear with the brakes on but not in neutral? Also, the ses light is not on.