urges Xtrail's head rectification?

I have a 2003 Xtrail and after the tuning I have failed me when I turned it on, but when putting D or R it is removed, at the beginning it was about twice the week it already has a week of doing it daily (only when it contained, advanced and it is removed), a mechanic tells me that it requires rectifying the head of the engine because it is wetting spark plugs, another mechanic says that they are only spark plugs but it has not seen them. PHYSICAL EXAM (NOT BY DIAGNISTIC OF APPLIANCE), I would like to get out of doubt because it is a lot of money about the recitification so that they are only spark plugs at the end of the case ... what do you think?

I would like to know what spark plugs look

They are white are not burned.

I guess you will have already done the adjustment of Taqest and there are no explosions in the admission or the escape, if so, I think it is a ignition problem, don't I know right now what kind of ignition it carries? But whatever it is to check it.

Good morning
, I know (and I don't know much about this) when the head of an engine is rectified, what is achieved is to remove some decimates from it and does not influence anything so that the vehicle has any failure.
They can be according to my knowledge several things

that
the bug spark plugs have or did not put those that this engine model carries ((I lean for this)
the joints of the spoiled valves
that are not the tuning well

all this influences that it stains the spark plugs or spend engine oil

.