after 1 month air filter dirty

[accy]

Hi
My audi a4 1.9tdi for the last 6 months has been very poor on performance and fuel.
It used to do 43-47 mpg local trip and now im lucky if it does more than 30mpg. The performance is also down.
Had the car fully serviced 2 months ago and made no difference but did notice less than a month after the air filter was filthy so replaced it. Checked the air filter again today and its filthy again.
What would be causing this? I assume its the reason for poor performance/economy.

Forgot to mention on cold startup it idles rough at 1000rpm for a few seconds before it settles down

[Guest 2]

Is it a genuine filter you're using?

[accy]

all genuine parts from tps.
Forgot to mention on cold startup it idles rough at 1000rpm for a few seconds before it settles down

[Doctle Odd]

Did you give her a scan with VCDS?

[accy]

Thanks for the reply.
Scaned with vcds no codes came up

[Doctle Odd]

Ok You'll need to check all the vacuum pipes for cracks loose joints etc. Also check the fuel filter. Does it pull ok? You could also clean the EGR valve

[accy]

Will check the vacuum pipes tomorrow. The fuel filter was replaced on the last service 6 months ago and the egr replaced 4 months ago all genuine parts

[Doctle Odd]

Where do you live mate? Did you change to a cheaper/different fuel supplier?

[accy]

live in n/e lancashire always fill up at shell ( loyalty points)

[Doctle Odd]

Not exactly sand storm country! you should check the pipes leading into the air filter for cracks splits etc