Nissan Repair: unstable idle Checkengine on, vacuum leaks, intake holes

Question
Dear Von,
my 91 300zx none turbo suddenly Unstable idle and its running not too good, 2 months ago when check engine light on I did replaced the 2 O2 sensors and its seem ran very good but last 2 days happen so I change a new fuel pres. regulator do the same, last night i trouble shoot by unplug the spark plug connection one by one I found that 5 plug I unplug are idle engine drop down except one when i unplug the spark plug connector note that the engine never feel idle drop(no Change)I change a new plug still the same, So Could You please tell me what is wrong or problems from the fuel injector its self? If so How do I replace the injector.
Best regards.
Lang

Answer
Lang,

Get a screwdriver and place the handle on your ear and the other end on the injector.  With the engine running it should click.  You can compare it to another injector to see that it makes the same noise.  It probably does.  But, I think you are on the right track so to change the injector I would remove the fuel rail by taking the bolts loose.  You do not have to disassemble the system.  Just pull the injectors up, evenly, until they all come out of the intake.  Now, on the one injector you are going to replace you will need to nuplug the clip for the electrical connection and then pull the clip that holds it on the fuel rail.  Buy a new injector or one from the wrecking yard, my favorite, and replace it.  You will need to get all new rubber o-rings for all the injectors and replace the lower ones that go into the intake.  First, you will get vacuum leaks if you don't and second the injectors are difficult to push back into the intake holes if you do not.  Be sure to coat the rubber o-rings wiht 30 weight motor oil to aid installation.  For some reason the 30 weight oil does not eat the o-rings and WD40 and the like does.  So, if you want to change the one injector and not have problems down the road this is the way to go.