i need help, bad.

[i want a 5.0]

i have a 1988 gt with alot of mods, converted to mass air, 12.1 pistons, 600 lift roller cam ect,ect, i drove this car for a month it idled at 1400 rps all the time, now the dam thing will not idle, i can set the idle while its running and it will be fine, shut it off and restart it and it will slowey die, will not idle,set the idle again and it is fine till i shut it off and restart and no idle. i am a certifed mechanic and am going nuts with this problem, any help would be great, it does not surg at all it will idle all day till i shut it off, its like the puter is forgetting where the idle is. thanks randy