won't idle warm or cold

hey, i posted my issue on TGO too but i havent had much luck so here it goes. ..
body- camaro '87
engine- 3.1L '92
tranny- t5 '92
did an engine swap in october and kept the SD setup from the 3.1 engine, i did all of the wiring to mod it with the 87 car harness. the car ran fine except for a 1500 rpm idle, smooth though
after a really cold night last week i went to start up my car the next morning and started off fine, got about 5 minutes into my drive and pulled up to a stop sign and the idle dropped to 500rpm or so, dash lights flickered a little bit then engine stalled completely. to restart i had to punch the throttle a bit otherwise it would just crank.
i noticed that the battery has a 13-14v charge after i let it sit when i was used to it being 12v on the dot.
The issue has persisted since then and ive checked the vacuum(21lbs hot)
timing(11* adv.)
cleaned out the dizzy
replaced coolant temp sensor
cleaned out IAC motor and segment of throttle body that it goes into

the thing that gets me most is that it will run ok sometimes in 40* weather, but at night (30* or so) it acts up like i mentioned
recently it does not even hint with the low idle, it will just drop off completely

any help would be great
thanks fellas

running rough at cold temps brings me to choke issues right off the bat. did you switch carbs with the new motor or use thee one that came with the new one? the pull off on my 91 f-bird is vacuum but its a 305. is yours electric?

its actually a FI intake, i see where you're coming from though, its so much easier to work on a motor when you dont have to fight with the stupid electronics lol

when you do get it to run, does it throw a code at all, does it smell like it's running rich or anything like that? I'm 100% that your problem is electrical/computer related.

it does smell like its running rich , if i put my hand behind the tailpipe and pull it away to smell i can smell the gas a little. i think it may be that my ECM thinks my IAC pintle is somewhere other than where it is so i have to check it out next time i have some play time, i think youre right though about it being an electrical issue