I have been searching but could use more input. I have a 1999.5 Pathfinder with 106K miles. Automatic. I am getting P0302 and at idle it runs rough and seems to misfire. But when I give it gas and get going it seems to run fine. When I pulled the #2 spark plug it was pretty black and seemed fouled out. I replaced it and it kept doing the same thing. Code came on about 50 miles later and spark plug was black again.
History: About a month ago I replaced timing belt, water pump, belts, and hoses. It was running great after that. I was getting an intermittent code P0138, for the Bank 1 Sensor 2 oxygen sensor. I did the extra ground mod but that didn't help.
Also, I had put some fuel cleaner in my gas over 2 fill-ups a few weeks ago just for the heck of it. It was some time after that when I started to notice the rough idle, but with no codes. Then last week I replaced that o2 sensor wondering if that might help. The P0138 code has not come back. Shortly after that I got the P0302 code. It mainly comes on if I let it idle for a while. The only thing I have done is replace the fuel filter.
Spark plugs are NGK and wires, cap and rotor all are Denso and all have around 5K miles on them. It seems to be getting spark to the #2 plug as well.
Also, I am getting the buzzing noise like the one mentioned in this thread:
Humming sound from rear when car is off - Nissan Forum | Nissan Forums (nicoclub.com)
I am leaning towards it being the #2 injector but it seems I am going to have to remove the intake manifold just to check or replace it. Unless there is a way to ohm it out without removing the manifold.
Any advice would be great.
