Fault code/repair?

I own a 05 2005 1.9 dlx citroen berlingo van,the engine diagnostic light comes on intermintly i have got a fault code reading of p0170.
The light only comes on occasionally and may be on for a second or two then goes out,the van has covered approx 55,00 miles and does'nt miss a beat.
I have cleaned the egr valve out and this seems fine.
The light has only started to come on /off since cam belt/water pump was changed.
I am using a non genuine air filter could this be an issue?
Any Help as this is getting tedious to say the least!