Nissan Repair: Rough running... still......, air control valve, broken bolts

Question
replaced the fuel injector as discussed last time. Noticed that all of the spark plugs look covered in carbon. It's got 150k on it so I suppose this may be normal. At the tail pipe sounds a very rhythmic missing sound. I also noticed a hissing sound from the back of the engine. It will go on and off very predictably. Very frustrated right now, any advice? EGR valve moves good so no issue there. Where else can I check?

Answer
Daniel,

If the EGR valve is stuck off its seat it will cause the engine to run rough.  Also, check to see if there are any broken bolts on the exhaust manifolds. Or leaks in the exhaust.  These will cause differences in the O2 sensor reading and that will cause the idle to jump up and down.  Lastly, check the idle air control valve.  This is located on the intake by the throttle body.