I have an 88 780 six cylinder non turbo. It has been running great for years and just started to missfire. I replaced the plugs with ngk irridium, new cap and rotor, checked fuel pressure running at 35 psi, and still misfiring at idle, and a huge loss of power at 1500 to 2000 rpm's. I have a really good understanding of vehicles, but this car is kicking my butt! Please, anyone have any ideas?:confused :

 

You may have bad wires. Which engine do you have? You may want to post this in the 760 section, I believe they have the same motor. You would also want to post milage and the last time the wires were replaced.