So, I got the dreaded Code 33 and code 45 after removing my MAF screens. I took it to a shop and they diagnosed everything according to GM and even changed the 02 sensor and nada. Code 33 means something may be wrong with the MAF. Code 45 means that it's running rich. You know what finally fixed the problem without buying a new maf? Spraying the MAF with MAF sensor cleaner. Both codes disappeared and it hasn't come back. Granted, it's only been a few weeks of driving. But a $7 can of MAF cleaner was worth experimenting with vs. the $300 Bosche MAF.