I have a 2005 z71 that recently went in for a coolant leak and rough idle. They found the water pump was leaking and replaced the o2 censor. After that it was still rough. so they replaced the intake gaskets and checked all the injectors but they were good. The motor is misfiring on all four cylinders on the drivers side and it spits out a black watery mix from the exhaust and smells like rotten eggs. so any ideas would be appreciated.