Simon,
I was quoting from the Haynes manual I have for my Ti6 +4. See point 7. I guess it varies by ECU engine etc
John
Evaporative emissions control
6 To minimise the escape into the
atmosphere of unburned hydrocarbons, an
evaporative emissions control system is fitted
to models equipped with a catalytic converter.
The fuel tank filler cap and vents are sealed
and a charcoal canister is mounted in the
engine compartment to collect the petrol
vapours generated in the tank when the car is
parked. It stores them until they can be
cleared from the canister via the purge valve
into the inlet tract, to be burned by the engine
during normal combustion.
7 To ensure that the engine runs correctly
when it is cold and/or idling, and to protect
the catalytic converter from the effects of an
over-rich mixture, the purge valve is not
allowed to open until the engine has warmedup, and is under load; the valve is then
opened to allow the stored vapour to pass
into the inlet tract.
8 On 4-cylinder engines the vacuum supply
to operate the purge valve is regulated by a
purge control valve solenoid which itself is
under the control of the ECU. The solenoid is
mounted either separately within the engine
compartment or, on later models, directly on
top of the charcoal canister.
9 On V6 engines the vacuum supply to the
purge valve is regulated by the constant
vacuum control valve (under ECU control) and
by a thermostatic valve which is opened or
closed depending on coolant temperature
