What about plug WIRES? They get old and degrade.And cause misfiring.

You mention the distributor was replaced last year.  There has been
some posts regarding oil leaks into the distributor once it's been
changed.

Bill

The reason why you won't have a vibration problem at higher engine speeds is
the flywheel effect. With the engine turning a couple thousand RPMs the
weight of the rotating mass means it's virtually impossible to the motor to
exhibit any momentary slowing down or speeding up - the "inertia" of all
that rotating steel is too much to allow you to notice any slow-down taking
in such a short taime frame. Then your engine will seem to "run smoothly" at
highway speeds (or even maybe at 40 MPH) but will be noticably rough at an
idle.

It's the easiest thing in the world to dump a can of injector clearer into
your gas tank and it only costs $5 to $7 for the best cleaners. I've been
using "Sea Foam" injector cleaner lately which was highly recommended around
here, and it seems to work okay & costs $5 per can. Be sure to put a can of
that in the tank when the tank is near empty - and then fill your tank with
gas so it can mix with the cleaner. DON'T put a whole can in unless you are
gonna put a lot of gas in on top of the cleaner.

Around here we usually need to special order Nissan parts like injectors
from the largest dealer who is also a big representative for Nissan. But
there are now auto parts dealers online who may give you a better price.
Injectors should be quite common - but a lot of manufacturers are trying to
get rich by selling high priced parts.

It seems possible your car mechanic may be trying to "rook" you. He ought to
be able to read the computer error code (I'd guess) that almost assuredly IS
an available diagnostic aid for your vehicle. That was how I knew my 97 p.u.
truck had an injector problem & the error code even said it was with the #4
cylinder injector.

Later I bought a neat little computer diagnostic tool that's even BETTER
than trying to "read" the flashing Check-Engine light as it puts out the
error code. This diagnosis tool is the "Scan Tool" (or ScanTool) and is
available from the "ScanTool.net" web site. This gizmo's input connects to
your vehicle's computer plug-in socket and the other side will plug into a
port (serial port) on your computer or laptop. With this ScanTool little
circuit board and a cable you also get the computer program you need to READ
those errors. This is absolutely great!!!!! there are a couple different
models for vaious manufacturers, and mine (most foreign cars) is the OBD-2
type. This stands for "On Board Diagnostices vers. 2".

***BAD MANIFOLD AIR FLOW METER***
I'd forgot about this - but 3 years ago a problem developed that my Nissan
truck Manifold Air Flow Meter went bad. This made my 97 p.u run very rough.
I was NOT able to *read* what that problem was by reading the flashing Check
Engine light as is usually possible. But when I plugged-in the ScanTool and
did that test with a computer it told the M.A.F. meter was BAD. (This was a
bummer!!) I finally got a replacement MAF which had to come from a Nissan
dealer = costly.  I'd looked at numerous used parts dealers online but could
not find an exact replacement model MAF meter to replace mine. In the end I
had to pay about $432 plus tax for a new one at the authorized Nissan
dealer.
  HINT: you *can't* (always) simply replace the plug-in electronic module
portion of the MAF Meter and expect the engine to run right. Each electronic
module (less than the size of a pack of Luck Strike) is specifically
adjusted for the airflow charactoristics of the "throat" of the precisely
machined aluminum flow meter body.

By taking my old electronic module apart, I found that water had entered it
and there was corrosion and "gook" on the circuit board. When installing the
new unit a bunch of silicone bathtub caulk was applied on it to keep out any
water.