I purchased a 2006 cobalt ss/sc with 2.8 and other mods, haven't messed with it alot yet, AFR is high and likes to stall when idling. I'm going to clean the MAF and throttle body and do the plugs this weekend. I scanned for codes and this came up... I was wondering if it's the manifold o2 sensor or is the Catalyst converter one.

P0132 - O2 Circuit High Voltage (Bank 1, Sensor 1)

 

It's going to be the one before the cat on the manifold.

 

That's the one that controls rich and lean right?

 

If it's lean and likes to stall, check for air leaks after the TB/MAF. Pics of your setup may help.

Also, if it's got a 2.8" pulley, what injectors are in it and what tune?