i just swaped in a 99 motor into my 98 gt, i built it with forged internals, comp 274 cams, comp springs Ti retainers, bbk l/t's bbk catted h-pipe, underdrive pullies. i swapped it in and itr wors fine i got it dyno tuned by a real reputable tuner and the WOT tuning was done in like 30 min. but he couldnt get the car to hold an idle, eventually we got it to idle ok but if you rev it, when the rpm's come down it trys to stall. it doesnt do it every time, only sometimes, its weird! any ideas?! we spent 6 hours on the dyno so were damn sure its not the tune, something mechanical maybe, the IAC works fine, please help!

 

ttt

 

ttt

 

from what you say . i think what your trying to say is that is idles ok but now and then when you rev it. the idle goes really low and almost stalls. still could be an iac valve sticking. or maybe the nature of those cams? i dont know but i have vt stage one cams, andthey do a similar thing but. if i rev them the idle will sometimes dip down low but always comes back to normal .

 

Possible computer relearn is needed. I'd drive it for 100 miles and see what happens. That's what I'm doing with my car. After a PI swap I can't hold an idle. When the idle starts to come down it almost stalls.