N62 4.8is- Engine REBUILD after Valvetronic/Vanos issues/codes

[StephenVA]

Test test test NOT guess guess guess
Idle vacuum fluctuating (SP)?
EGR vacuum pots clean and operational?
Smoke tested entire intake system for leaks?
Cleaned the throttle body plate and replaced the mounting gasket?
Cleaned & Replaced the cam sensors seals?
Removed and replaced all the plugs with known good NGK plugs?

Recommendations:

There are three plugs recommended for the 4.8is from NGK

OE NGK ZFR6FH-11, Stock number 4294. Iridium 0.8 center electrode with a platinum ground electrode plug. Factory gap of 0.044 inches

Iridium IX NGK ZFR6FIX, Stock number 6441 Iridium 0.6 center electrode Tip (copper core) with a cut back and tapered platinum ground electrode plug. Factory gap of 0.044 inches.

The big difference between the OE plug and the IX is the additional engineering and trimming steps to provide better anti-fouling, easier cold starts, better tip in acceleration, and the shells are coated with anti-corrosive and anti–seizing materials.
The recommendation is always go with the plug that will provide the best performance over the widest range of driving. In our applications I would go with the NGK Iridium IX plugs every time. Will the smaller center electrode wear faster? Yes, in a lab. You will get 60K out of them easy.