I have a 2000 with 3.0 L V6 that after warming up seems to "sigh" at the stop lights. The more it warms up the more " sighs" it lets out at the stop signs. I'll pull up to the light and put in the clutch car comes down to an idle and then sighs. Next light it might do 2 or 3. The more she warms up, the more of them she does. I've counted as many as 14 on arriving back at my driveway. The ECM shows 505 code so I replaced the IAC and it came back........Any Ideas??..............THX