Getting missfires during cold start

Maintenance/Repairs
1

Honda civic lx 2009 (R18 1.8L) turbo’s and 350cc injectors with hondata tune.

During cold starts while idling I’ll get a couple sputtering sounds. The air fuel gauge goes from 15.4 to 17.3 where it becomes rich

If I drive under 2500 rpm’s it won’t really missfire to much after little bit of heat, but if I try boosting while not hot, it’ll missfire like crazy and in all cylinders when we put a scanner on it.

Once it’s completely hot/running temps I get 0 missfires. The tuner wasn’t sure why it’s only misfiring cold, my guess is the Honda needs a valve adjustment after I put one step colder plugs and tune on it. But anything else that may cause a non-isolated misfires?

2

15.4 AF to 17.3 is lean to very lean. Both would cause misfires. With E10 gasoline your idle AF should be in the area of 14.2 or so or a Lambda of right at 0.97 to 1.0.

Why is your tune so lean at low inlet air temps?

3

Have you taken a look at the coolant temp readings from the computer? When you first start it from cold, coolant temp should read around ambient air temps. And it can be off/wrong, but if not in an “implausible” range wouldn’t set a code. But it’s important to the AF mix. Not likely the issue, but easy enough to check.