Had a strange  problem that my FG xr6 turbo would have a misfire when the car warmed up or sat for a while after driving around. And it was very intermittent, nothing in particular would cause the same problem.   Checked plugs, ignition coils, wiring, battery, earth cables, connections to coils and injectors all seemed fine. I thought it might have been the coil drivers in the PCM so was ready to set the car on fire..     Long story short, clean your connections first.