EDITED: first off thanks to fieroguru, DavidGXP, and GXP25 for their research in this area the FSM GXP25 provided was the last unknown for this swap turns out my alldata Ls4 wiring diagram was wrong, so i deleted it out of the original post please disregard quotes of the orginal in posts mentioned below..
Courtesy of GXP25
**This is a general guide ALWAYS verify your year TB pinouts first**
PINOUTS ARE AS FOLLOWS
LS2 GTO TB . LS4 TB
PIN A ---- PIN F
PIN B ---- PIN E
PIN C ---- PIN H
PIN D ---- PIN A
PIN E ---- PIN B
PIN F ---- PIN D
NOT USED PIN G&C ON THE LS4 HARNESS
**If you have idle surge or hanging idle see below
http://youtu.be/WI-RuRQ1nDc
PARTS LIST:
TB adapter here 55 USD http://www.alpermotorsports.com/inde..._detail&p=1688
Pigtail: LS2 Throttle Body Pigtail Brand New LS2 TB Pigtail | eBay
Throttle body: Ebay got mine for 140 shipped
all bolts are m6 x 1.0 you will need 4 for the TB and 3 are included with the TB adapter to the intake manifold
Thickness of LS2 TB for bolt length
Adapter
For issues with idle like i eventually had you will need to adjust 2 tables in the pcm
ETC scaler and Base idle airflow need to be adjusted to get you idling right.
here are the values i used with good sucess results may vary.
