Did some work.. now have some issues

[Lynx331]

Hey guys, i recently did some work to my 87 gt, now im having a few issues with it. I converted it to mass air, and did some work to the top end of the motor. The only problem is now my car is averageing about 10 mpg. The parts that are on the car, i got from a friend who was making at least 15 mpg with the setup. The car smells like its running very fat at idle, but when i pull a plug it is white, which indicates the car is running lean. The computer that is in the car is a A9P, dont know if that makes any difference or not. When i scanned the computer as a 1989, it gave me code 91 ( o2's not switching ). But i couldnt find out if the o2 was staying on lean or on rich. Is there any way to test an o2 sensor? Could the o2 sensor cause this? I am still running stock injectors, and a stock MAF meter. Im thinking about taking the MAF meter apart and cleaning it. Ive heard that if dirt gets on the wire it will make the car run bad. I dunno what to do here guys.. what do you think?

Thanks!

 

[ss93cobra]

Depending on what parts were used to convert to mass air you may have to switch some of the pins around in the computer plug in that involve the emissions system. Sorry, I can't recall specifically which wires. They are for t.a.b. and t.a.d. as well, which could certainly cause your concern. What did you use to convert to mass air? A "kit", or just parts gathered up?