The vehicle has been to the shop twice already.
First visit: Replaced mass air flow (MAF) sensor. Replaced air control valve.
Still ran rough.
Later generated codes: 0171 and 0174, lean bank 1, and lean bank 2.
Also misfires detected (pending codes), but this may have been a by-product of the rough idle condition.
Second visit: Replaced intake plenum gaskets. Replaced spark plugs.
After soaking in the cold for several hours, upon start up the engine runs very roughly. It shakes and chugs for a long time. Sometimes it tries to hold an idle, then drops very low and runs very roughly.
When it's warmed up, it runs fine.
At high idle or when accelerating, it runs fine.
What's the next step?
I read somewhere about warped plastic on the plenums? Or blown a PCV valve? I think this stuff has been checked already. I don't think the engine would run at all if the PCV valve was blown out.
What could be wrong?

 

https://www.mazdaforum.com/m_90020/tm.htm

See post #4

Opus