[2SS Capt]

Originally Posted by KingLT1

Just to clarify, It's not a lean or rich issue. It's an airflow and torque issue. Again, these ECM's are torque based on this platform. If something in the system changes to where it changes the airflow, then the torque will change, and the ECM will compensate with timing adjustment. Some throttle bodies have more idle airflow then stock, so the ECM pulls timing to get back to its programed torque range. The fix in this situation is to go into the VTT table and reduce torque in the idle area of the map and the ECM will raise timing. Low timing increases heat. Negative idle timing can make the headers glow red. That is what can potentially hurt cats. Again, it's not a lean issue because in closed loop the ECM will correct the AFR via fuel trims up to 30% to achieve stoich afr.

I agree, but if there is a huge "notch" in the Throttle Body allowing a LOT more air to go past at idle, the ECM has to do something, either add more fuel (making idle a LOT higher to match the airflow), or retard the timing to keep things in check while heating up things beyond design specs.. Either way, NOT a good thing... No idea why they added that huge uncontrolled notch, but I'm not an engineer of these things, just merely making an educated observation, but it sounds like it may cause issues if not tuned properly for all the extra air at idle...