Car skips and dies down & sounds like it's back firing when 1st started . on 1993 Lincoln Town Car

it dies down to about 7mph after a few blocks it catches up and will drive fine. does the same thing when you stop and it's sits for a while b4 starting engine again. car will also die down after a steady speed (like if you use the cruse control for a while. the check engine will come on and off during driving as well. We keep all the oils checked and changed every 3K to 5K. We use the high grade of gas as well but nothing seams to help.

Asked by for the 1993 Lincoln Town Car