I got an intermittent p0121 code over the course of 6 months or so. I have multiple throttle bodies laying around and decided to put on what I thought was a stock tb instead of cleaning my stocker. It was off of my 12 sierra denali when I upgraded it to an ls3 tb. I pulled it out thinking it was identical and quickly realized it was slightly different. I went ahead and put it on but the idle in park and neutral surged up to 2000 rpm and wouldn't idle down even after driving it for a week to week and a half. I found the thread about the difference in throttle bodies so I changed the etc scalar in hpt to what my stock denali tune was as well as the percent max and percent max-brake to the 12 denali stock values (this happens to be the same as 09 tbss's). The idle was slightly better but i would have to stop in gear before putting it in park for around 10-12 seconds before the truck would suddenly idle down 2-300 rpm then I could put in park without it idling up. I decided to see if a gold blade ls3 would react any differently. I changed the etc scalar and percent max/percent max-brake to the stock camaro values and swapped tb's. This helped a little but it still had the same issues as the 09 up truck tb. Fast forward to today I cleaned my stock tb and of course it runs perfect even with the camaro values still in the tune. I will re flash it with the stock values but it runs perfect. I guess my question is gm obviously upgraded the tb's in 09 for a reason and assuming they are better in some way, why do they react so weird with the 08-older operating systems and what else needs to be changed to get say a gold blade ls3 to work with an 07 os? And yes I have read old threads all the way back to 09 on here and hptuners and they all just either say it worked great, or don't do it because it will never work right. But most just say etc scalar is all that needs to be changed. Well that doesn't work with mine for some reason. The G8 guys have similar issues since the platform ran over that 08/09 model year. Alvin and Kelly had no problem tuning my sierra denali with an ls3 tb but told me they feel the stock tb is the best with our trucks unless you go FI or some radical setup, so what's different? Is it the opening rate of the plate that causes the weird idle? Why do some tuners say it will work great and other say its total waste. Why do some of our trucks have zero issues and other literally can't get them to work? And I know this has been covered to death as far as if it will or won't work but I couldn't find any of the reasons why.