Wish I had investigated a little further when mine had that little "spell" a while back...1997 3.1 LS, it began with the CEL coming on, then I noticed the idle was just a bit more rough than the normal smooth as glass...but when you trounced it, man did it respond! Felt like I gaided 25 hp or something...
There was a dip in fuel economy, but not terrible.
I don't remember the code numbers it set, but they were "Fuel Trim Rich" and "Coolant Temp Outside Expected Parameters" or something like that...
But the problem went away after a couple of days, and I never found out the cause.
Wouldn't have minded having a switch to flip to put it in that mode on demand
