SKODA OCTAVIA GLXi 2 Litre (reg Dec 2000)

I have a problem with fuel consumption- it has returned between 10MPG and 20MPG over the last 6 months (as indicated on the trip computer). In Sept 2005 it had its 40K service and had a misfire corrected by fitting a new Air Mass Meter, the MPG returned to a more usual 36-37MPG.

In Dec 2005 it had its MOT and passed on the Exhaust Emissions Test. In early March 2006 it was investigated for low MPG (10MPG) and fitted with a140839461B Lifter, after finding that the breathing system was blocked. Pipes to the PCV valve on air inlet pipe cleaned out. MPG initially returned to normal figures but over the next four weeks fell again to 20MPG overall. In mid April 2006 car returned to main dealers (as always) who

This is a pretty long shot, but if you are parking the car in the same plaec maybe something is blocking things up.

I'd open up the air filter box and make sure the filter is clean and then follow the pipes to the intake making sure there are no blockages. After that I guess check fuel filter has been changed recently and try changing petrol stations just incase you are getting a tank of cr*p. I had to install a fuel filter in an old fiesta as supermarket fuel was just so bad it couldn't cope. (I was utterly stunned as there appeared to be sand in it when i changed the filter).

These are just the cheap and easy DIY checks you can do, but I am sure somebody else will be along who knows more about the engine to give you a proper answer soon.

EDIT: Actually you mention the breather system is blocked. It isn't being overfilled with oil or to thin an oil is it?