P0300 NISSAN - 1999 Mercury Villager 3.3 Misfiring, we can't fix it!

Question

I have a 1999 Mercury Villager with the 3.3 engine, and a bad miss at all rpms, and it will stall at idle.
So far we have replaced:
-The distributor, brand new, with new cap and rotor, OEM exact fit,
-All new high quality wires,
-New platinum plugs gapped correctly (the old ones looked fine and were the correct brown color),
-New fuel filter,
-New intake gaskets,
-New knock sensor.
-Fuel pressure is good at 45 psi, and goes up 7-8 psi when the vacuum line is removed,
-Timing has not jumped, and was checked,
-EGR valve checked and is also good, not stuck open.
-Plugged the EGR opening in the intake, and no change.
No vacuum leaks either, checked all the hoses.
-TPS was checked and is good also.

We are at our wits end, any help would be so appreciated.

Answer 1

Been there done that,This Nissan engine has the popular injector terminal problem,just pull a connection ,there corrosion at the terminal,There is also a TSB update on these wire for the injectors,TSB 03-22-06.(update injector wiring harness)The injector connection is the most likey of your misfire.There is also the MAF sensor that has been known to cause drivability problems Its a poor ground at the MAF,The ground can be repaired by soldering a 16 gauge wire to the ground at the MAF.The next other problem that is know on this vehicle is in the distributor,it uses a optic sensor oil tend to get in there,if its oil contaminated clean it out with brake cleaner.And by the way since your in the distributor make sure the rotor is in its correct position and is secured.Also look at the ignition coil its in the distributor it has a tendency to ark to ground,P300 when I have these on the Mercury Villager it always been the ditributor coil,which reminds me there has always been a popular failure and that is the connection of the distrubuto connection not on the distributor but on its tail end if it loose the 1 degree signal it misfire under load,and stalls out.