Starts fine! Then runs rough until choke goes to idle

[Steve Hartman]

2007 5.4 ltr 197K miles. My car starts just fine! And it runs fine for about 10 seconds. Then, as the (choke?) slowly opens and the engine moves down towards normal idle, my car coughs and sputters like it had Covid or something. Then, once it gets to normal idle my car returns to its lovable, fine running self. Any guesses?
Thank you!

 

[JimR_TN]

My wife’s Equinox had a similar issue. Started great, after a few seconds the idle would drop as it it went to closed loop using the O2 sensors to control A/F ratio. It would die and wouldn’t idle until it was fully warmed up. Turns out it was a bad O2 sensor 1. It was still working, but not well and only worked right when hot.

Not sure yours is the same but it does sound like your issue occurs when the engine switches to closed loop using O2 sensors.

 

[Steve Hartman]

A fine starting point, Jim! Thank you! And I just happen to have a trusty O2 socket! IF, I can find it! LOL! Is there a way to read the O2 sensor with a meter?

 

[Adieu]

Dirty throttle body or recent battery replacement/full discharge? That loses throttle "learn" settings.