1999 Lincoln Navigator miss fire at idle

Engine Performance problem
1999 Lincoln Navigator V8 Four Wheel Drive Automatic

engine miss fire at tick over on gas switch to lpg
engine runs smoth have ijector signels and new ijectors as we found No 3 not ticking and showing open loop on scan when in take manifold was off and pipe work out the way we changed plugs so we have 8 new plugs


feed back info on lincon town car heater all good and working ok thans Dave Keeling