Cheers TB, I have been looking for set of values for the maf for that engine but I can't find any Merc ones. I always worked off idle = engine size, so it's a bit low.
I was hoping someone on here knew what other engine sensors the ecu effectively ignores(if any) when the maf if unplugged. Other than that I'm thinking post maf air leak, I know some of the bigger engines Mercedes make are prone to the inlet gaskets leaking a bit, but I can't find anything on an R-class as they didn't sell many I guess!
The odd thing though I'd the fact it holds the throttle open a bit sometimes, only an extra 1 or 2 degrees but it shuts it back to idle setting as soon as you unplug the maf.
I am open to the idea that he's bought a duff maf, even if it was over £200. Especially as the faults all disappear when you unplug it, however it runs almost identically (live data also) on both maf's.