There is a vacuume solenoid on the carb that kicks up the idle and prevents stalling on these units when the steering or hydraulics are deadheaded.
Make sure that the DASHPOT is functioning correctly and adjusted correctly and your problem will be solved. Test the part with a vac pump to make sure the it holds vac. check the vac source from the manifold and make sure that is good.
Common occurance on these more often than not just replacing a worn out or adjusting will fix the problem.
Naturally you will need to make sure that your gov, Idle, and other settings INCLUDING ENGINE TIMING are set correctly.
Typically NOT a Hydraulic or Engine Issue, particularly based on the reading you are indicating.
Good Luck
Scoot (22 Year Nissan Dealer)
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