What to do? My car is running rich, tooooooo rich

[SilverSpear]

I took my car to the yearly government checkup this saturday and it failed because of the tyres (cracked and I didn't notice them ) so I got back, tried to install Yokohama AVS's but the specs I wanted were not available at the moment (235/40/17), so I had to put Toyo's and they look and feel great (135 US$ per tyre). So I got back to the checkup and it passed this time.

Now the second problem is that the CO2 level showed disturbing news and the guys over there told me that I might have a NON WORKING MAF .

The acceptable level of CO2 emitted (there are no exhaust restriction in my country... whatsoever) for the fuel to burn properly is 12% and above. Last year it was 6.06% and this year it got into 3.67%... and I am really noticing overconsumption from one year to another... So guys what to do? where might be my problem here?

Another issue is that there is no garage here which tests the CO2 level, they do not care about it, there is only the government place which shows this measure. People go here to check on the CO and not CO2.

I am thinking of going by LAN's Stage 2V5 with the 300Z MAF and if necessary and applicable add a fuel management system to the combo for better results...

Any help from the technical gurus???