codes 172 and 176. help?

ok, so my stang has been randomly flashing the cel at me lately, so i went ahead and pulled the codes.

it gave a

172 - heated exhaust gas oxygen sensor - voltage indicated lean (bank 1)
176 - heated exhaust gas oxygen sensor - voltage indicated lean (bank 2)

ok. super. that prolly explains or at least has a hand in the car randomly deciding to detonate a lil and throw the cel.

so, what should i do now? go buy new o2s? could something else be causing the codes. btw these were the only codes present.

thx

well i went out and cleaned the mas. didnt seem too dirty, started up fine, drove it around, and like usual the cel came on more or less randomly, and then off, then on etc. it comes on without much reason that i can see, itll flip on/off during throttle, light throttle, no throttle, and itll stay on/off for random amounts of time. some days itll be off for 30 mins then on, other days itll come on and off every 5 mins in the exact same driving conditions (commute to and from work). sigh.

also, there doesnt seem to be any vac leaks, so how would i go about checking over the ect and iat inputs?