Nissan Repair: engine, mass airflow sensor, nissan pathfinder

Question
1990 4WD Nissan pathfinder 3.0
When I pulling popup trailer I cannot keep speed limit on strait road. When I drive it without trailer it feels just fine. Ideles fine, no misfire.
When I put meter on MAF output I am reading at idle 1.7 V   when I press the pedal it goes up 4 volts.
Sometimes it just wakes up and I can go 90 m/h
I looked in Mitchell it said readings should be 1.0-3.0 Volts on MAF output. I got one from Autozone it does the same thing. What can be wrong with Nissan? Why it does not have power?

Answer
Andrei,

Basics are in play here.  It is not he mass airflow sensor.  I would first check to make sure the plugs are good.  Nippondenso or Autolite double platinum are great for added horsepower.  Cap, rotor and wires are good and the filter is new.  Next, make sure the timing is correct.  Get a K & N airfilter and replace the old paper one.  Your timing should advance to give you more power so check to make sure the optical shutter wheel on the distributor is good.  A 1990 should be on its way out.  Use 5W30 motor oil to get more power too.  I am sure after this many years the rings are getting worn so I like Mobil 1 synthetic to aid in oil control.  Check to see that hte converter on the exhaust is not plugging up and that the muffler is not falling a part inside.  I like Flowmaster mufflers for additional power without the noise.  Lastly, make sure you are using good gas and a fuel treatment would not be a bad idea.  The knock sensor will not advance timing as much with cheap gas.  If the injectors are plugging up this would lean out the mix and the power will drop off.  The fuel pressure is correct?  Email me back and let me know.  I know I have listed many things here but without looking at the vehicle these are just a few of the things I have found.