When To Change The Air Filter?

[bonjo]

my 2003 petrol has been giving me ace fuel consumption till recently.Having moved from the countryside to urban area, the mpg has gradually dropped from around 33 to 28. Now some of it is expected because of the type of journey I make; but:

Today I checked the air filter,which has done around 15k and looked very grey! It is worth getting a new one anyway? Not sure what the replacement interval is?

Any suggestions?

[anchorman]

For what they cost you could change it but you can expect less fuel economy now you are in the town and the weather is getting colder.

[bonjo]

I think I'll do this anyway even if it is as an experiment to see the effect (if any).

We are also between summer and winter fuel grade, some stations already have the winter fuel,some are still selling summer grade.

Will keep you posted :)