[TR] cam idle update

[Randall]

> Advancing the spark in this way occurs through two mechanisms: vacuum and
> mechanical. Vacuum is created as the engine runs. More acceleration = more
> vacuum. 

Er, well, actually it's the other way around.  Vacuum is created by closing
the throttles and impeding the flow of fuel/air into the engine; at maximum
acceleration (throttles wide) there is very nearly no vacuum at all and
hence no vacuum advance.  So, the vacuum advance (if present, most TR6
didn't have vacuum advance) is maximum at cruise (no acceleration at all)
and is primarily a device to improve fuel economy.

Randall