I have a Buick with this issue and I haven't figured it out yet. I'm hoping to get a clue here. I never thought of the fuel injection fuses. A lot of Caddy's and Buicks have another set of fuses under the hush panel on the passenger side. I don't know if the 84 Deville does or not. You should try to find those fuel injection fuses though. It does sound like the fuel injectors just aren't getting power like mine.