Unstable cold start idle

2009 GMC Sierra 4.8- Using HP tuners

A few days back I started playing with HP tuners on my truck. Had to do an entire write on the ECM due to disabling VATS. Also increased transmission MPH shift points up 3MPH. Other than that nothing else was done. The issue I'm having is during cold starts when coming off the gas pedal the idle stumbles and will stall. Is there an electronic throttle relearn process or something like that due to the entire rewrite? What else should I be looking at. Its an E38 EMC

Steve

Not sure if it applies to you, as it's more a carb' trick, but some manufactureres use a damper on the throttle return to stop it closing completely on sudden throttle lifts, to prevent stalling out. If there is one on your engine, check it's adjusted and working correctly.

Another possibility is there is a fuel shut off that's playing up and/or poorly mapped.

It could be an air leak, which is more evident in the over-run when manifold vacuum is the highest?

Is it worse when you use the brakes, as there may be a fault in the booster/servo check valve?

Something else.

The truck is drive by wire. Not any worse during breaking. The only thing that has or was changed is the ECM rewrite