Trip computer that Shows average speed and fuel consumption very irratic. I have a Toyota Corolla T3 2005.

What does a ten plate mean.

best at 10 liters per 100 klms , average around 12 liters /100 klms
fuel consumption depends largely on load , speed , operating conditions , towing, highway/city, off road so an exacting answer is not possible as it all depends on the operator and the driving skills

do a complete tuneup plugs coils air filter and put some fuel additive in your gas tank seafoam is the best

fuel consumption of engines is a question very often asked and seldom answered adequately. There are so many variables that affect consumption so I will give a few
tyre pressure and size
ambient temperature
condition of engine
load carried
number of passengers
weight of driver
dragging brakes
extras on vehicle (roof rack)
wheel alignment
tread pattern of tyres
driving habits
speed
driving conditions (town-country)
driving conditions ( hilly --flat)
road surfaces
slipping into neutral at lights
the list goes on and on so be guided by the expected average of the manufacturer of between 8 litres to 10litres per100kilometers travelled

There are five trip computer displays which may be stepped through by pushing the MODE button. The information will appear in the following order:

D AVG ECON (Average Fuel Economy): This shows the average fuel economy since the last reset.

D INST ECON (Instantaneous Fuel Economy): This shows fuel economy for the most recent second of driving.

D RANGE (Trip Range): This shows the estimated distance that can be traveled with the remaining fuel. The fuel economy used to calculate range is based on the last few hours of driving. When in a low fuel condition, LO is displayed.

D FUEL USED (Trip Fuel Used): This shows the accumulated fuel used since the last reset.

D AVG SPEED (Average Speed): This shows the average speed since the last reset.

You can download a replacement Owner's Manual here: 2002 Chevrolet Impala Owner's Manual (PDF file from www.gmownercenter.com)

only use the first third of the gas peddle
use premium grade fuel(computer controlled engine will adjust for better fuel quality)
TURN OFF THE A/C uses about 25% of your fuel.
sorry to say this, but next time buy a smaller engine/body car (in england, if it dont do more than 45 mpg,as an average,the residual value is pants...)

why does my normal rpm always bug down when the engine start?and when I started to use the air con, the rpm was playing. It doesnt go on a certain point. it always range at 800rpm then it will down to 700. what am I might do to solve this probem?

Its not a clock its just calculates the time it took to make trip. The display at the bottom of the tachometer area is a "TRIP COMPUTER". It shows OUTSIDE AIR TEMPERATURE, DISTANCE TO EMPTY, AVERAGE FUEL COMSUMPTION, AVERAGE SPEED and JOURNEY TIME. Press the "TRIP" button on the steering wheel to change through the modes. Holding the "TRIP" button for more than one second will reset the mode.

you have switched the trip computer to instantaneous fuel consumption rather than average.the switch on the end of the wiper stalk.press the switch until you get back to average consumption ,i think it shows a circle with a line through it from memory

dont get technical just drive it and it wont go wrong then