After a air mass flow sensor failed I have had an increasing occurance of smoke blow at startup. It is a black wispy smoke, not a foggy cloud like oil at all. I don't know why I think this as I have no experience but I thouht it seemed to me like a rich fuel mixture smoke and only lasts 1 sec at startup.

It started getting worse to the point it happened everytime at startup and was fairly heavy. Then we had a check engine light come on, followed by the engine temp never coming up.

Had the dealer do the simple thermostat replacement and they verified the code was for the same. They said that they would normally replace the ECT (Engine Coolant Temp) sensor as well but it was out of stock (additional $50).

Puff of smoke went away, engine temp comes up fine now, and mileage as improved according to the trip computer so I am sure we were running low temp for a while.

Now a couple weeks later the puff of smoke is starting to appear again. Not nearly as bad/thick as before this time, but it looks the same to me.

Any ideas?
Is the temp guage on the console fed from the ECT or could the ECT be bad?
Could it be anything else?
They will replace ECT at no additional labor.