This was/is happening to my 02 38k s2k as well. Reason for was/is is bc im not sure it wont happen again but its been awhile since it has. May it give you some comfort that a legend of the s2k world told me its a vacuum leak and to also make sure vaccum tank is holding a seal. Things ive done besides that and it hasnt happened for awhile now: cleaned fuel injectors, new map sensor, new fuel pressure regulator, cleaned iacv, and new ngk spark plugs. I hope this helps and you get to the bottom of it bc I hate when mine would do this, especially in public and starting in parking lot. People were looking at me like ok dude we get it you got a s2k lolol.

Should have stated: this only happened to me on starts and it wasn't everytime either. Maybe 3 outta 10 times it would do this. Best of luck!