[mysocal911]

Originally Posted by Flat Six

Not sure if I understand your last bullet point; are you saying this same DME w/stock chip did pass CA smog previously? Or that it does now?

Sounds an awful lot like an idle mixture issue to me. A couple of thoughts:

1) O2 sensor doesn't affect mixture until engine is warm and in closed-loop mode, you might want to connect a DVM to it though to get a general sense of cold idle mixture.

2) Just because CHT is new doesn't mean it's sending proper signal to DME; I'd measure resistance at connector to double-check its function. If OK, I'd still check at DME connector to ensure there isn't an issue w/wiring or connector(s) along the way.

3) Didn't see it mentioned, but is ICV working properly?

4) Smaller vacuum leak(s) can manifest as idle issues but less obvious when engine is warm and DME can adjust mixture. You might want to check all the usual suspects, especially for a new build check/re-tighten intake runner bolts. A vacuum gauge here can be very helpful.

5) Also might want to check your plugs for both signs of rich mixture and whether they're the proper heat range. BTW, which plugs are you running?

6) Did you verify/adjust the idle screw at the throttle body? I'm sure you know this, but as a reminder, short the B/C terminals when you do.

Hope this helps.

Read post #20 here; Bench testing Carrera Idle Control Valve