A couple of weeks ago the fuel consumption on my VRS dropped dramatically, where before on a run I would regularly get 42/45mpg, and low to mid 30's around town it has dropped by at least 10mpg on each (lucky to get 30mpg on a run).

I've had no engine light, no fault codes (checked regularly), no dragging brakes, correct tyre pressures, changed the maf (told by local Skoda dealer it's a common fault that doesn't always throw up a code).

It has a stage one map, sports cat and single box stainless exhaust, K&N panel filter in a de-finned air box with a 3" cold feed, all of this was fitted before my consumption dropped, oh and my driving style hasn't changed.

102K miles with full history and I bought it when it was 18 months old and had 9K on the clock.

I first thought that a Lamda sensor had gone down but surely that should throw a fault code!

Any ideas

Checked your breather pipes? Also is the power still the same?

Faulty coolant temp sensor? Leaking exhaust or split manifold?

clogged fuel filter maybe?

Have you had the battery disconnected?

Tyre pressures?, flux capacitor? More info on what you've checked and the general performance would help

have you brimmed the tank and actually checked what MPG you are getting? I wonder if you've got a software issue making out the MPG is low?

Performance the same, warms up fine, idles fine, no exhaust leaks and I brim the tank normally twice a week and work out the consumption the old fashioned way, and with the cost of Shells finest getting ever more expensive I want to get it sorted.

The only thing I haven't checked is the breather hoses, I know they're prone to rotting (my son has a Leon Cupra on which I've replaced a couple), but would they have such a marked effect on the amount of fuel the car uses?

Possibly. If you have a split breather hose then it'll be sucking unmetered air into the manifold through the split, the engine then runs lean (too much air not enough fuel) and if the lambda sensors pick this up the ECU will try and compensate by injecting more fuel to bring the mixture back to normal.

Re. the coolant temp sensor - you could swap sensors with your son for a couple of days (same sensor on the 180bhp Leon Cupra) if his MPG goes down then you can swap back and buy yourself a new one.

Thermostat is another possibility.

I was losing maybe 5-10mpg due to overfueling when my manifold breather was split

Cheers guys, I'll check the breathers today.

It's a good excuse to fit some Forge silicon ones, especially as they're only 2 miles from my front door .