1998 nissan navara efi sensor problems

lots of causes, can name 50
but low fuel pressure tops my list. fuel filter packed.
get the car serviced.
(or clogged map of maf sensors)
wow it ran for 23 years (magic that)

do they revs drop off when taking pressure off accelerator pedal when out of gear? if only staying high during gear change it would suggest a worn clutch friction/pressure plate so the engine isn't slowing down when clutch is depressed .I'd also have the OBD codes read to see if there is a sensor/switch at fault , but sounds like the clutch to me

Spark plugs won't cause this kind of problem. It sounds more like the oxygen sensor in the air intake is faulty. You may be lucky by just cleaning the connector from the sensor or cleaning the sensor itself. It may be contaminated with dust etc. Otherwise it will mean a new sensor. Very simply, the oxygen sensor tells the EFI system the best air/fuel ratio to set at different throttle settings.

Check for fault codes for the idle speed sensor,accelerator position sensor and crank position sensor

your burning oil the plugs probably need replacement ---and the oil can cause fluctuation in rpms ---carbon valves --problems with o2 sensors --clog cat converter-foul plugs etc

SOULDS LIKE EXCESSIVE EXHAUST BACK PRESSURE CAUSED BY A RESTRICTED CAT CONVERTOR. SHOULD HAVE NO MORE THAN 1.5 TO 3 PSI CHECKED AT THE O2 SENSOR AT IDLE AND AT 2500 RPM. THE CONVERTOR CAN BECOME DAMAGED IF UNBURNT FUEL ENTERS IT. THIS IS CAUSED BY TUNE UP CONCERNS USUALLY.

heve utried adjusting the trottle , just put your foot on the accelerater and hold at just under 1000 revs if shaking goes then thats your problem should idle at just under 1000rpm

Sounds to me like you have a leak somewhere in the intake system. The idle fluctuation sounds like a vacuum leak- and of course, when the turbo spools up, you have positive pressure replacing vacuum. Look for a loose hose clamp or a torn hose, etc. etc. By the sounds of it, you shouldn't have any trouble finding the leak.

Nissan Scope Certified Technician- 10 + years experience in Nissan dealership

vacuum leak......bad tps.......bad mass airflow meter system........any of those are suspect...... also check for bad ground at battery to be sure all is not computer freak out from bad readings ...good luck

run the fault codes
look for ambient temp sensor or baro sensor problems