You are the first person in 10,000 questions I've answered that put a Youtube link to show results of their tests. Its hard to say what is going on. Look for vacuum leaks, sometimes misfire code criteria is pretty high before a fault code is actually set, my suspicion if it were an Infinity Q45, some VW and Audi, or Lexus RX300 ,and Camry or V8 Jaguar would be to say a coil is breaking down even thought the misfire code is not set. I wonder could you have a dirty injector that once the engine warms up the fuel atomizes better and makes the engine perform better. Nissan Maxima and Pathfinder had problems with Mass Air Flow meters and many after market replacements were junk. Do you have a workshop manual. Alldata is best. The information is year make and model specific, covering repair procedures, torque specifications, fluid capacities and specifications, service bulletins, component locations, wiring diagrams ect.... Alldata is very easy to navigate http://bit.ly/AllData_Repair_Manuals_Online
Your intake manifold vacuum is good!If you drove the car with a vacuum gauge taped to the windscreen with the engine under constant load (not wide open throttle ) the vacuum readings would be smoother.
Thanks for replying Patrick. I've had coil issues on my BMW and this doesn't feel like it (there's no jerkiness typical of a misfire). I checked coils for corrosion when changing plugs and they looked good. My MAF is aftermarket (made by Altrom) and has worked fine for the last 6 months FWIW. I have the Nissan workshop manual and it's nearly useless. And I forgot to mention, I run seafoam in the gas tank every 3-4 months. Just did the seafoam crankcase and intake treatment too. It idles smoother, but the hesitation persists. My initial suspicion was a leaky or stuck open EGR as the symptoms are similar (power loss at low rpms and at WOT). Unfortunately I can't hook the vacuum up to it to test b/c it's hardlined into the intake manifold. Is this possible? probable?