I have a 99 Grand Prix GTP with IS3 Cam/Heads, Northstar TB, 60/65 lb injectors, SLP headers, & other supporting mods, no IC yet though, also I removed the EGR completely.
Ever since I installed the Northstar TB & 60/65 lb injectors (along with editing the PCM for such changes) my car has had a surging idle, let me elaborate...
When I start the car up on a cold day (colder than roughly 30 degrees) the idle with surge up and down for a few minuites.
The colder it is ouside the worse the surging is, i.e. when the temp is like 10 degrees or colder the car will surge from about 600 rpm to possibly 1800 rpm for about 5 minutes, After a few minutes the engine finally smooths out and gets to stable rpm, the warmer it is the less severe the surging, at around roughtly 30 degree or warmer the surging is barely noticeable.
I set the idle via my HPTuners to about 900 or so.
I have dealt with the issue for a few years now but I would like to know if anybody has had a similar issue of a surging idle & has found the answer & fixed it.