Well had a P0172 (rich condition) come up on my 2010 LT 2.2L HHR... When my car was in the shop for a lean condition. IT was traced to the upstream sensor not reading right and fuel trim readings not where they should be. Put new one in and everything was reading like it should. Four months later its now reading rich and it pointed to the same sensor (upstream) not reading correct again. What would cause a sensor to go bad in a matter of months.

 

It most likely never was the sensor. P0172 means the sensor IS working. There are other codes for the sensor being bad.

 

What else would you check on the car? We have checked for air leaks about 3 to 4 times and that is counting from being in three shops (finding no vaccum leaks).

 

The MAF sensor being dirty could cause that

 

Fuel pressure, bad injector, dirty MAF, cracked flex pipe, burned valve, MAF connector
https://www.obd-codes.com/p0172
https://www.obd-codes.com/p0171

And remember; rich does not always mean rich. Here is one of many results from "fuel trim" in Yahoo, it is really involved.

https://search.yahoo.com/yhs/search;...&hsimp=yhs-004
Short Term Long Term Fuel Trim Explained

 

An OFF question but you dont happen to have an aftermarket air intake do you?

 

That is discussed in at least one of my links.