I just had a chuckle at this, on page 4 of the Driver’s handbook for my
SIII V12 saloon:
"During prolonged urban use, where the engine speed remains consistently
low, carbon deposits are built up in the combustion chambers.
Subsequently, as the engine speed is increased to high performance
levels, the deposits will be quickly dispersed; this may be apparent by
a brief period of detonation accompanied by some blue smoke from the
This condition is normal and is no cause for alarm."
It is the combination of the words “detonation” and “no cause for alarm”
that tickled me. And yes, the way to resurrect a V12 that has a stumble
at idle is to take it out for a good hard thrash - but fancy putting the
words in that form in the handbook!