Why my 03 maxima idles high after 20 to 30 miles

SOURCE: High idle

The throttle position sensor may be causing your issue----This sensor monitors the outside air temp.In the winter the throttle opens up far because th.e air temp is cold and vice versus

SOURCE: 95 maxima rough idle

The injector could definitely trigger a misfire code, but you also mentioned that you had a mass airflow sensor code , that code code be responsible for te sluggish moment of the vehicle and rpm going up and down. However if you have a misfire onCyl#6 and the coil and the plug is good the ONLY other thing to cause a mis-fire would be the injector. To check the injector get a NOID light, you can get one at almost any auto-parts place. To use unplug injector plug from the bad injector and connect it to NOID light the light should have a steady PULSE/ligt flickering. If light flickers fine then injector is bad and will need to be replaced. If light doesn't flicker or flickers intermittently then you may have a bad wiring to that injector. Check if wiring is good, then you may have a bad cam sensor or sensor gear. Good Luck and contact if you need more help. Thanks for using FIX YA

SOURCE: 1992 SE maxima jerking, sputtering, stalling

I had a similar problem and resolved it by replacing the mass airflow sensor. Ive got 235k+ miles on my 1992 Maxima SE.
Still runs good but having problems with the alarm system.

SOURCE: rough idling lack of power

Try replacing the fuel filter.
Check for a vaccum leak

SOURCE: 1995 Nissan Maxima idle problems

Let's try the cheapest fix first. Change the fuel filter out. You'll probably see a brown looking goop in the gas, This is an "ETHANOL" problem. Read up on it. These are all related to so many idle and acceleration problems. Buy a can of SEAFOAM at the parts house. Fill up tank with Premium and add SEAFOAM. Then change filter out before 500 more miles. This should clean out the water and the goop and the carbon build up caused by the ETHANOL. Add a can of SEAFOAM every 3000 mile after that to a full tank of gas. It will keep your emissions,engine, and fuel lines clean. And will keep your car from line freeze up. Good luck.