I havbe already replaced the pre-cat and air filter and had a emmsions flush and my CEL keeps coming back. Mazda is telling me that i have a bad air mass meter. The code they are getting is P0170. Autozone gets a P0171 code and the guy at Autozone is telling me to replace my 2nd O2 sensor.. Any advice???

Mine got 171 code. No matter if it's too lean or too rich, it could be either of the O2 sensors or MAF sensor, ECU needs info from both to adjust the mixture.

How much did it cost you to replace the pre-cat O2 sensor?

I repalced the actual pre-cat convertor, not the O2 sensor. I think I will try to replace both O2 sensors first. You can get them for around $75 a piece at www.oxygensensors.com. I can not find a MAf sensor on the Internet for sale.

I cleaned the MAF and the light is gone.