Just replaced intake on 2008 Grand Marquis LS , 4.6 with 120 k on it. Original FORD intake was leaking coolant under the thermostat housing. I replaced intake, thermostat, water pump, serp belt, and spark plugs, cleaned throttle body with correct spray. I replace plugs with Motor Craft Platinum plugs, checked gap and all were at .054---When job was complete, I primed the fuel rail turning key on and off 3-4 times, after that, car fired right up with no issues. After 1/2 hour of running in Park, I decided to drive car around the block. As I pulled threw the intersection and accelerated, the car shook and stumbled like all heck. I returned home, checked that there was no vacuum lines disconnected, and that all corresponding wire connectors were correct to each injector and coil on plug. Again, while car is idling in Park, it runs perfect, when you gas it in drive, it stumbles and the exhaust smells like sulfur. I have yet to get an engine light to come on. Any help greatly appreciated...car ran perfect prior to me replacing intake, car had original motor craft plugs still in it.