In article ,
Andrew May wrote:
I had a similar thing with my Metro which also used the A series engine.
I was told that it was 'Dieseling' and that this was caused by carbon
build up on the cylinder which heated up to the point where it would
ignite the compressed mixture without a spark (in the same way that a
Diesel engine works). So after turning off the ignition and depriving
the engine of a spark it would continue to ignite and hence 'run on' for
a short while.

It can be carbon, but the combustion chamber is sort of heart shaped and
the peak between the two valves can glow red hot causing the petrol to
ignite without a spark. Relieving this peak by grinding can help.

There are however people on this group much more knowledgeable about
cars than me and I am sure they will be along in a moment.

--
*Seen it all, done it all, can't remember most of it*

Dave Plowman London SW
To e-mail, change noise into sound.