[radz28]

Generically adding to Josh', these cars operate off torque modeling (and have for a while, and if you know this - sorry - just trying to justify my statements, however a beginner I am). The ECM is calculating torque, during all operation, based off fueling, because that's a constant (I thought it was airflow, but I read one of the Big Dogs on HPTuners [like GHuggins/Higgs Boson/Howard Tanner/etc.] said otherwise, if I recall [I just found the post by Tanner stating IT IS airflow, but I've read elsewhere it is fueling; I'm not sure how much it matters either way, necessarily, as the point is to calibrate correctly), so you're actually adding airflow to the fuel. But there is a direct correlation with fuel and torque, so you're adjusting airflow, through the throttle body, to match the fuel you want, because you're making a torque request through the accelerator pedal (it's even more complicated, to me, for turbo cars, which I'm playing with).

So - for all these systems to balance (ECM playing with the TCM, playing with the CCM for fuel pump, Traction Control/Stability Control/ediff'/Drive Modes/sub-modes, etc), they have to speak the same language: torque. So - when you push the accelerator pedal down 25%, the ECM might think you're requesting 400-lb.ft. of torque, and it will open the throttle (throttle body blade) to, say, 50%, because that's the torque the ECM is calibrated, by GM, to correspond with for that speed, at that RPM, in that gear (Driver Demand table), for 400. So the ECM will open the blade to the calibrated opening to achieve the airflow rate that it's calculating you are requesting. These sensors are not measuring the actual air particles that enter the throttle body. There are correlations that they have made by GM during development, and can be calculated, so long as there are constants they can go by. So...

... If you change the airflow enough, the torque model is no longer accurate, which means a lot of the other modeling is off. If it's off far enough, for example, at idle, the car could start trying to retard so much ignition timing, you'll melt your cats', because the change in airflow you made with the bigger TB is telling the ECM that to much torque is being made. If that torque exceeds the stock torque modeling (in the VTT), it's going to try to reduce torque. And the easiest way to do that, at idle, is retard timing (because you can only close the blade so much, and the ECM can adjust the timing so much faster than with the blade) - which can get low enough, perhaps, that you start melting things because the combustion process is now happening later enough in the cycle that a lot of the heat has moved from the combustion chamber toward the exhaust port, and that pushes too much heat into the cats'. So - changing airflow too much might push the ECM out of it's calibrated range to calculate torque accurately.

Were it me: I would do what it takes to monitor timing advance at idle (preferably more, but I'm staying with idle to keep from making this post longer) and make sure it's enough that you're not getting too low. Some people say keep it not too much lower than 10*, for example, but definitely not close to 0*, or you're into trouble.

Too much. Sorry... I'm rushing the response, so, please, don't roast me much, experts, lol.