Problem fixed! It was #6 COP. Leaving this post for others. Easier to get to than some of the others.

2000 E-150 5.4, 208k miles

Today I had a pending code of P0402 but it never coded after one hour. Previously I've had the codes for left and right banks lean several times but not today. Also P0306, misfire a few months ago, but just once.

My code reader is Bluetooth so I can monitor some sensors. O2 bank 2 sensor 1 was 1.3 volts opposed to bank one's 0 volts, but after 30 minutes, it went to 0v like bank 1. No change in idle or driving.

I bought a new COP for #6 but I wanted it to show me that code again before I replace it. I've had COP failures before but I think #6 is original.

It idles rough until 1000 RPM, then its smooth. Driving it, its really rough. Low on power. Smells like sulfer.

EGR and if so, what's the usual problems with it? Going out right now to look at how easy #6 is to replace cause if it's easy I'll just do it.

I put fuel cleaner in it as that has fixed my lean banks before and I put it in with a low tank so it was a lot.

 

Back to both banks lean (P0171, P0174). Maybe the MAF next?