air leak.

go and do a MOT emissions test and post results for me please

and you didnt buy a new MAF you bought a recon MAF (unless it was a dealer genuine they are all not worth a wank am afraid )

Also Lambda`s only have a maximum of 60,000miles life like a timing belt so if its done more than 60k, change the sensors for genuine Bosch ones ASAP (BOTH)