What would the running symtoms be Mike?
low power retarded feeling over heating as will be burning wrong mixture, the 02 sensors would be trying to trim the mixtures with restricted airflow,
my question would be how many miles has car done, if over 60k would check timing chain for wear as well as popping off the inlet manifold, all this bull that is put around where some have said the n18 was better and they improved the timing chain issues,, the chains are still same part numbers as all the other prince engines from 2006 to present, only thing they have changed is the chain tensioner so rather than upgrading the chain ie the main issue,, they make the tensioner longer so people might not have chain failures until over 80k more so,, reality is i have seen n18 with chains fail as low as 30k if run low on oil if treated hard it would seem, most common still around 60k.. where it stands out is when you drive one that has had chain done and realise just how retarded it has been running with a stretched chain in it before,, ie a car that has no fault codes as bmw/mini also done software updates to broaden the spectrum of where it would throw up a EML for timing fault codes i would guess,
when chains are stretched the over lap on the inlet to exhaust valves as changed and this can add to the carbon effect on the rear of valves also if car breaths a lot ie vapour out of the oil filler cap as this gets fed in to the breather that enters the inlet manifold to be fed back into the engine add the inlet valve open at wrong point allows hot gases to back track to inlet manifold causing carbon build up,, its a stupid design of the engine to use this method that needs correct valve timing set by the vanos sprockets so they dont use a EGR valve to cut NOX emissions and building costs... but most car makers are using same way
seafoam in engine oil can reduce the breathing cleans piston rings out and coats the inlet manifold as well,
