I just had my motor built. Had the tuner come down, and street tuned immediately to start the breakin.

It was warm all day long while the tuner was tuning, no issues w/ start up or idle.

Problem I have now, is on cold start up, the car will start, idle normal for about 3 to 5 seconds, sitting at about 13-15 INHg. Then, as the RPMs start to drop down to their normal idle, the vacuum starts going down, towards zero, and then the car just dies.

It'll do that continually until the car is up to operating temperature.

We messed w/ the IACV and such, and it didn't seem to be the problem.

Any suggestions? Is this just something that happens w/ fresh engines until they get a few hundred miles on them?

Thanks for any help.