Nissan Repair: 1993 Nissan Quest Surges, mass airflow sensor, intake plenum

Question
QUESTION: 1993 Nissan Quest shudders/surges especially under hard acceleration especially from 1st gear.  Noted fairly thick looking disconnected 1.5 ft. vacuum line with 'U shaped' fitting coming up from off top of trans-axle...is this the problem? Where does it attach - it seems just a bit too short to connect to intake plenum - does it connect to another section of vacuum hose which fell off it ??  Could it be too dirty air cleaner or dirty fuel injectors contributing to the shudder/surging??

ANSWER: Peterboy,

The hose you describe is for venting the differential and to preclude water entering the housing.

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QUESTION: In your opinion what would be the most likely cause of the surges/shudders?  The van has been tuned within the last year (wires/plugs/cap/rotor) and now has a new fuel filter and air cleaner.  Coil going out?  Fouled fuel injectors?  Transmission going out?  Engine seems to idle and run smoothly and rev well when not engaged with drive-train (Neutral or Park), yet surges/shudders interject most noticeably when drive-train is under load: accelerating briskly or going uphill. Generally there's no problem on level ground with low-to-moderate accelerator depression, and van will accelerate to 65MPH as long as not pushed too hard in which case the it will begin to shudder/surge, as if something  is wanting to hold it back.  The problem has been getting gradually worse over the last six months and the van now starts 'balking' quite consistently when pushed up steep hills!  Thank you very much for your knowledgeable answer in advance!!

Answer
Peterboy,

CHeck the mass airflow sensor and the distributor for the presence of oil on the optical pickup and shutter wheel.  Also, the van is known for breaking motor mounts and if you get into a loaded situation the engine will rock back and forth giving one a sense of hesitation when it is just the engine moving about.