This is out of the Get to know your GTO literature that came with the car.
Premium unleaded fuel with an octane
rating of 91 or higher is recommended
for best performance. Using regular or
middle-grade fuel of 87 octane or higher
is permissible, but the vehicleís acceleration
may be slightly reduced. If fuel
with an octane rating of less than 87 is
used, you may hear a heavy knocking
noise that can damage your engine. In
this instance, you should fill the fuel tank
with higher-octane fuel as soon as
After fueling, ensure that the gas cap
is installed correctly and tightly. If it
is loose or missing, the malfunction
indicator lamp will light steadily. If a
loose gas cap is the cause, a few
driving trips after properly tightening
the gas cap should cause the light to
go out. If the light remains on, have
the vehicle serviced.
See Section 5 of your Owner Manual.